/* Tailwind utility replacements (replaces CDN) */
.min-h-screen { min-height: 100vh; }
.flex { display: flex; }
.flex-col { flex-direction: column; }
.flex-1 { flex: 1 1 0%; }

/* ==========================================================================
   CrackCode — ByteByteGo-accurate Design System
   ==========================================================================
   Structure:
   1. CSS Custom Properties (:root)
   2. Base reset & typography
   3. Layout (header, sidebar, content, footer)
   4. Sidebar chapter items with numbered circles
   5. Content typography (.lesson-content)
   6. Figures & diagrams
   7. Code blocks
   8. Buttons & cards
   9. Callout boxes
   10. Utility classes
   ========================================================================== */


/* ==========================================================================
   1. CSS Custom Properties
   ========================================================================== */

:root {
  /* --- Brand Colors --- */
  --color-primary:        #149F76;
  --color-primary-hover:  #0F7F5E;
  --color-primary-dark:   #0D6B4F;
  --color-accent:         #35CEA0;
  --color-accent-hover:   #2AB88D;
  --color-active-green:   #8DDEB9;
  --color-active-circle:  #23A067;
  --color-footer-link-hi: #35DDAC;

  /* --- Neutral / Text --- */
  --color-text-primary:   #282828;
  --color-text-secondary: #333333;
  --color-text-tertiary:  #666666;
  --color-text-muted:     #999999;
  --color-text-inverse:   #FFFFFF;

  /* --- Backgrounds --- */
  --color-bg-white:       #FFFFFF;
  --color-bg-page:        #F9FAFB;
  --color-bg-code:        #F6F6F6;
  --color-bg-footer:      #404040;

  /* --- Borders --- */
  --color-border-light:   #DEDEDE;
  --color-border-medium:  #AEAEAE;
  --color-border-heavy:   #D4D4D4;
  --color-border-code:    #E5E5E5;
  --color-footer-divider: #5C5C5C;

  /* --- Border Radius Scale --- */
  --radius-sm:            6px;
  --radius-md:            12px;
  --radius-lg:            24px;
  --radius-pill:          100px;

  /* --- Spacing Scale (4px base) --- */
  --space-1:  4px;
  --space-2:  8px;
  --space-3:  12px;
  --space-4:  16px;
  --space-5:  20px;
  --space-6:  24px;
  --space-8:  32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;

  /* --- Typography — System Font Stack --- */
  --font-sans:  -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
                "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue",
                Helvetica, Arial, sans-serif;
  --font-mono:  "SF Mono", Monaco, "Cascadia Code", "Roboto Mono", Consolas,
                "Courier New", monospace;

  /* --- Font Size Scale --- */
  --text-xs:   12px;
  --text-sm:   14px;
  --text-base: 16px;
  --text-lg:   18px;
  --text-xl:   20px;
  --text-2xl:  24px;
  --text-3xl:  30px;

  /* --- Line Heights --- */
  --leading-tight:  1.25;
  --leading-snug:   1.375;
  --leading-normal: 1.5;
  --leading-relaxed: 1.625;

  /* --- Font Weights --- */
  --font-normal:    400;
  --font-medium:    500;
  --font-semibold:  600;
  --font-bold:      700;

  /* --- Layout --- */
  --header-height:    64px;
  --sidebar-width:    320px;
  --content-max-width: 820px;

  /* --- Shadows --- */
  --shadow-sm:  0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md:  0 2px 8px rgba(0, 0, 0, 0.08);
  --shadow-lg:  0 4px 16px rgba(0, 0, 0, 0.1);

  /* --- Transitions --- */
  --transition-fast:   150ms ease;
  --transition-base:   200ms ease;
  --transition-slow:   300ms ease;

  /* --- Callout Colors --- */
  --callout-info-border:    #3B82F6;
  --callout-info-bg:        #EFF6FF;
  --callout-tip-border:     #149F76;
  --callout-tip-bg:         #ECFDF5;
  --callout-warning-border: #F59E0B;
  --callout-warning-bg:     #FFFBEB;
  --callout-danger-border:  #EF4444;
  --callout-danger-bg:      #FEF2F2;
}


/* ==========================================================================
   2. Base Reset & Typography
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: var(--font-normal);
  line-height: var(--leading-normal);
  color: var(--color-text-primary);
  background-color: var(--color-bg-white);
  min-height: 100vh;
}

img,
svg,
video {
  display: block;
  max-width: 100%;
  height: auto;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary-hover);
}

ul,
ol {
  list-style: none;
}

button,
input,
select,
textarea {
  font: inherit;
  color: inherit;
}

button {
  cursor: pointer;
  border: none;
  background: none;
}

table {
  border-collapse: collapse;
  width: 100%;
}

hr {
  border: none;
  border-top: 1px solid var(--color-border-light);
  margin: var(--space-6) 0;
}


/* ==========================================================================
   3. Layout — Header, Sidebar, Content, Footer
   ========================================================================== */

/* --- Header --- */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  height: var(--header-height);
  background-color: var(--color-bg-white);
  border-bottom: 1px solid var(--color-border-light);
  display: flex;
  align-items: center;
  padding: 0 var(--space-6);
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  max-width: 1400px;
  margin: 0 auto;
}

.site-header__logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-lg);
  font-weight: var(--font-bold);
  color: var(--color-text-primary);
}

.site-header__logo:hover {
  color: var(--color-text-primary);
}

.site-header__nav {
  display: flex;
  align-items: center;
  gap: var(--space-6);
}

.site-header__link {
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--color-text-secondary);
  transition: color var(--transition-fast);
}

.site-header__link:hover {
  color: var(--color-primary);
}

.site-header__link--active {
  color: var(--color-primary);
}

/* --- Mobile hamburger button --- */
.site-header__menu-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  color: var(--color-text-primary);
  transition: background-color var(--transition-fast);
}

.site-header__menu-toggle:hover {
  background-color: var(--color-bg-page);
}

/* --- Sidebar close button (mobile only) --- */
.sidebar__close {
  display: none;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  color: var(--color-text-tertiary);
  margin-bottom: var(--space-4);
  margin-left: auto;
  transition: color var(--transition-fast),
              background-color var(--transition-fast);
}

.sidebar__close:hover {
  color: var(--color-text-primary);
  background-color: var(--color-bg-page);
}

/* --- Page Layout --- */
.page-layout {
  display: flex;
  min-height: 100vh;
  padding-top: var(--header-height);
}

/* --- Sidebar --- */
.sidebar {
  position: fixed;
  top: var(--header-height);
  left: 0;
  bottom: 0;
  width: var(--sidebar-width);
  background-color: var(--color-bg-white);
  border-right: 1px solid var(--color-border-light);
  overflow-y: auto;
  padding: var(--space-6) var(--space-4);
  z-index: 100;
}

.sidebar__title {
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  color: var(--color-text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-4);
  padding: 0 var(--space-2);
}

/* --- Main Content --- */
.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  padding: var(--space-10) var(--space-8);
  min-width: 0;
}

.main-content__inner {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

/* --- Footer --- */
.site-footer {
  background-color: var(--color-bg-footer);
  color: var(--color-text-inverse);
  padding: var(--space-12) var(--space-8);
}

.site-footer__inner {
  max-width: 1200px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--space-8);
}

.site-footer__heading {
  font-size: var(--text-sm);
  font-weight: var(--font-bold);
  color: var(--color-text-inverse);
  margin-bottom: var(--space-4);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.site-footer__link {
  display: block;
  font-size: var(--text-sm);
  color: rgba(255, 255, 255, 0.6);
  padding: var(--space-1) 0;
  transition: color var(--transition-fast);
}

.site-footer__link:hover {
  color: var(--color-footer-link-hi);
}

.site-footer__link--highlight {
  color: var(--color-footer-link-hi);
}

.site-footer__divider {
  border: none;
  border-top: 1px solid var(--color-footer-divider);
  margin: var(--space-8) auto;
  max-width: 1200px;
}

.site-footer__bottom {
  font-size: var(--text-xs);
  color: rgba(255, 255, 255, 0.4);
  text-align: center;
}


/* ==========================================================================
   4. Sidebar Chapter Items with Numbered Circles
   ========================================================================== */

.chapter-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.chapter-item {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  height: 60px;
  padding: 0 var(--space-4);
  background-color: var(--color-bg-white);
  border: 1px solid var(--color-border-medium);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background-color var(--transition-fast),
              border-color var(--transition-fast);
  text-decoration: none;
  color: var(--color-text-primary);
}

.chapter-item:hover {
  background-color: var(--color-bg-page);
  border-color: var(--color-accent);
  color: var(--color-text-primary);
}

.chapter-item--active {
  background-color: var(--color-active-green);
  border-color: var(--color-active-green);
}

.chapter-item--active:hover {
  background-color: var(--color-active-green);
  border-color: var(--color-active-green);
}

.chapter-item--completed {
  border-color: var(--color-border-light);
}

/* Chapter Number Circle */
.chapter-item__number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  min-width: 32px;
  border-radius: 50%;
  background-color: var(--color-accent);
  color: var(--color-text-inverse);
  font-size: var(--text-sm);
  font-weight: var(--font-bold);
  line-height: 1;
}

.chapter-item--active .chapter-item__number {
  background-color: var(--color-active-circle);
}

.chapter-item--completed .chapter-item__number {
  background-color: var(--color-primary);
}

/* Chapter Label */
.chapter-item__label {
  flex: 1;
  min-width: 0;
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  line-height: var(--leading-tight);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chapter-item--active .chapter-item__label {
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
}

/* Chapter Status Icon (optional checkmark / lock) */
.chapter-item__status {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 20px;
  height: 20px;
  color: var(--color-text-muted);
  flex-shrink: 0;
}

.chapter-item--completed .chapter-item__status {
  color: var(--color-primary);
}

/* --- Section divider within sidebar --- */
.sidebar__section {
  margin-top: var(--space-6);
  margin-bottom: var(--space-3);
  padding: 0 var(--space-2);
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}



/* ==========================================================================
   5. Content Typography (.lesson-content)
   ========================================================================== */

.lesson-content {
  color: var(--color-text-secondary);
  font-size: var(--text-base);
  line-height: var(--leading-relaxed);
}

.lesson-content h1 {
  font-size: var(--text-2xl);
  font-weight: var(--font-bold);
  line-height: 1.3;
  color: var(--color-text-primary);
  margin-top: var(--space-10);
  margin-bottom: var(--space-6);
}

.lesson-content h1:first-child {
  margin-top: 0;
}

.lesson-content h2 {
  font-size: var(--text-xl);    /* 20px */
  font-weight: var(--font-semibold); /* 600 */
  line-height: 28px;
  color: var(--color-text-primary);
  margin-top: var(--space-8);
  margin-bottom: var(--space-4);
}

.lesson-content h3 {
  font-size: var(--text-lg);    /* 18px */
  font-weight: var(--font-semibold); /* 600 */
  line-height: 25px;
  color: var(--color-text-primary);
  margin-top: var(--space-6);
  margin-bottom: var(--space-3);
}

.lesson-content h4 {
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  line-height: var(--leading-snug);
  color: var(--color-text-primary);
  margin-top: var(--space-5);
  margin-bottom: var(--space-2);
}

.lesson-content p {
  font-size: var(--text-base);  /* 16px */
  font-weight: var(--font-normal); /* 400 */
  line-height: normal;
  color: var(--color-text-secondary); /* #333 */
  margin-bottom: var(--space-4);
}

.lesson-content ul,
.lesson-content ol {
  margin-bottom: var(--space-4);
  padding-left: var(--space-6);
}

.lesson-content ul {
  list-style-type: disc;
}

.lesson-content ol {
  list-style-type: decimal;
}

.lesson-content li {
  font-size: var(--text-base);
  line-height: var(--leading-relaxed);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-2);
}

.lesson-content li::marker {
  color: var(--color-text-tertiary);
}

.lesson-content strong {
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
}

.lesson-content em {
  font-style: italic;
}

.lesson-content a {
  color: var(--color-primary);
  font-weight: var(--font-medium);
  text-decoration: underline;
  text-underline-offset: 2px;
}

.lesson-content a:hover {
  color: var(--color-primary-hover);
}

/* Inline code */
.lesson-content code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  padding: 2px 6px;
  background-color: var(--color-bg-code);
  border: 1px solid var(--color-border-code);
  border-radius: var(--radius-sm);
  color: var(--color-text-primary);
  word-break: break-word;
}

/* Reset for code inside pre (handled by code block styles) */
.lesson-content pre code {
  padding: 0;
  background: none;
  border: none;
  border-radius: 0;
  font-size: inherit;
  word-break: normal;
}

.lesson-content blockquote {
  margin: var(--space-4) 0;
  padding: var(--space-3) var(--space-5);
  border-left: 3px solid var(--color-border-heavy);
  background-color: var(--color-bg-page);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--color-text-tertiary);
  font-style: italic;
}

.lesson-content blockquote p:last-child {
  margin-bottom: 0;
}

.lesson-content .table-scroll {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  margin: var(--space-6) 0;
}

.lesson-content .table-scroll table {
  margin: 0;
}

.lesson-content table {
  margin: var(--space-6) 0;
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-sm);
  overflow: hidden;
  font-size: var(--text-sm);
}

.lesson-content th {
  background-color: var(--color-bg-page);
  font-weight: var(--font-semibold);
  text-align: left;
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--color-border-light);
  color: var(--color-text-primary);
}

.lesson-content td {
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--color-border-light);
  color: var(--color-text-secondary);
}

.lesson-content tr:last-child td {
  border-bottom: none;
}

.lesson-content hr {
  margin: var(--space-8) 0;
}


/* ==========================================================================
   6. Figures & Diagrams
   ========================================================================== */

.lesson-content figure,
figure.diagram {
  margin: var(--space-6) 0;  /* 24px 0 */
  text-align: center;
}

.lesson-content figure img,
figure.diagram img {
  display: inline-block;
  max-width: 100%;
  height: auto;
  border-radius: var(--radius-sm);
}

.lesson-content figcaption,
figure.diagram figcaption {
  font-size: var(--text-sm);   /* 14px */
  font-weight: var(--font-semibold); /* 600 */
  color: var(--color-text-tertiary); /* #666 */
  text-align: center;
  margin-top: var(--space-3);
  line-height: var(--leading-normal);
}

/* Diagram container — optional wrapper for architecture diagrams */
.diagram-wrapper {
  margin: var(--space-6) 0;
  padding: var(--space-6);
  background-color: var(--color-bg-white);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-lg);
  text-align: center;
}

.diagram-wrapper img {
  max-width: 100%;
  height: auto;
}


/* ==========================================================================
   7. Code Blocks
   ========================================================================== */

.lesson-content pre,
pre.code-block {
  margin: var(--space-4) 0;
  padding: var(--space-4) var(--space-5);
  background-color: var(--color-bg-code);
  border: 1px solid var(--color-border-code);
  border-radius: var(--radius-md);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.lesson-content pre code,
pre.code-block code {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  color: var(--color-text-primary);
  display: block;
  white-space: pre;
  tab-size: 4;
}

/* Code block header (language label / copy button) */
.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-2) var(--space-4);
  background-color: var(--color-bg-code);
  border: 1px solid var(--color-border-code);
  border-bottom: none;
  border-radius: var(--radius-md) var(--radius-md) 0 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

.code-header + pre,
.code-header + pre.code-block {
  margin-top: 0;
  border-radius: 0 0 var(--radius-md) var(--radius-md);
}

.code-header__lang {
  font-weight: var(--font-semibold);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.code-header__copy {
  font-family: var(--font-sans);
  font-size: var(--text-xs);
  font-weight: var(--font-medium);
  color: var(--color-text-muted);
  cursor: pointer;
  padding: 2px var(--space-2);
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast),
              background-color var(--transition-fast);
}

.code-header__copy:hover {
  color: var(--color-primary);
  background-color: var(--color-bg-white);
}


/* ==========================================================================
   8. Buttons & Cards
   ========================================================================== */

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: var(--font-bold);  /* 700 */
  line-height: 1;
  border-radius: var(--radius-pill);
  transition: background-color var(--transition-fast),
              box-shadow var(--transition-fast),
              transform var(--transition-fast);
  white-space: nowrap;
  text-decoration: none;
  cursor: pointer;
}

.btn:active {
  transform: translateY(1px);
}

/* Primary */
.btn--primary {
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
}

.btn--primary:hover {
  background-color: var(--color-primary-hover);
  color: var(--color-text-inverse);
}

/* Secondary / Outline */
.btn--secondary {
  background-color: var(--color-bg-white);
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
}

.btn--secondary:hover {
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
}

/* Ghost */
.btn--ghost {
  background-color: transparent;
  color: var(--color-text-secondary);
}

.btn--ghost:hover {
  background-color: var(--color-bg-page);
  color: var(--color-text-primary);
}

/* Size variants */
.btn--sm {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
}

.btn--lg {
  padding: var(--space-4) var(--space-8);
  font-size: var(--text-base);
}

/* --- Cards --- */
.card {
  background-color: var(--color-bg-white);
  border: 1px solid var(--color-border-heavy);  /* #D4D4D4 */
  border-radius: var(--radius-lg);              /* 24px */
  overflow: hidden;
  transition: box-shadow var(--transition-base);
}

.card:hover {
  box-shadow: var(--shadow-md);
}

.card__header {
  padding: var(--space-5) var(--space-6);
  border-bottom: 1px solid var(--color-border-light);
}

.card__body {
  padding: var(--space-6);
}

.card__footer {
  padding: var(--space-4) var(--space-6);
  border-top: 1px solid var(--color-border-light);
  background-color: var(--color-bg-page);
}

.card__title {
  font-size: var(--text-lg);
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
  line-height: var(--leading-tight);
}

.card__description {
  font-size: var(--text-sm);
  color: var(--color-text-tertiary);
  margin-top: var(--space-1);
  line-height: var(--leading-normal);
}

/* Card as a link */
a.card {
  display: block;
  text-decoration: none;
  color: inherit;
}

a.card:hover {
  color: inherit;
}


/* ==========================================================================
   9. Callout Boxes (info / tip / warning / danger)
   ========================================================================== */

.callout {
  margin: var(--space-6) 0;
  padding: var(--space-4) var(--space-5);
  border-left: 4px solid var(--color-border-heavy);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  background-color: var(--color-bg-page);
}

.callout__title {
  font-size: var(--text-sm);
  font-weight: var(--font-bold);
  margin-bottom: var(--space-2);
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.callout__body {
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  color: var(--color-text-secondary);
}

.callout__body p:last-child {
  margin-bottom: 0;
}

/* Info */
.callout--info {
  border-left-color: var(--callout-info-border);
  background-color: var(--callout-info-bg);
}

.callout--info .callout__title {
  color: var(--callout-info-border);
}

/* Tip */
.callout--tip {
  border-left-color: var(--callout-tip-border);
  background-color: var(--callout-tip-bg);
}

.callout--tip .callout__title {
  color: var(--callout-tip-border);
}

/* Warning */
.callout--warning {
  border-left-color: var(--callout-warning-border);
  background-color: var(--callout-warning-bg);
}

.callout--warning .callout__title {
  color: var(--callout-warning-border);
}

/* Danger */
.callout--danger {
  border-left-color: var(--callout-danger-border);
  background-color: var(--callout-danger-bg);
}

.callout--danger .callout__title {
  color: var(--callout-danger-border);
}


/* ==========================================================================
   10. Utility Classes
   ========================================================================== */

/* --- Display --- */
.u-hidden       { display: none !important; }
.u-block        { display: block !important; }
.u-inline-block { display: inline-block !important; }
.u-flex         { display: flex !important; }
.u-inline-flex  { display: inline-flex !important; }
.u-grid         { display: grid !important; }

/* --- Flex Utilities --- */
.u-flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

.u-flex-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.u-flex-col {
  flex-direction: column;
}

.u-flex-wrap { flex-wrap: wrap; }
.u-flex-1    { flex: 1 1 0%; }
.u-shrink-0  { flex-shrink: 0; }

.u-gap-1  { gap: var(--space-1); }
.u-gap-2  { gap: var(--space-2); }
.u-gap-3  { gap: var(--space-3); }
.u-gap-4  { gap: var(--space-4); }
.u-gap-6  { gap: var(--space-6); }
.u-gap-8  { gap: var(--space-8); }

/* --- Text --- */
.u-text-xs      { font-size: var(--text-xs); }
.u-text-sm      { font-size: var(--text-sm); }
.u-text-base    { font-size: var(--text-base); }
.u-text-lg      { font-size: var(--text-lg); }
.u-text-xl      { font-size: var(--text-xl); }
.u-text-2xl     { font-size: var(--text-2xl); }

.u-font-normal    { font-weight: var(--font-normal); }
.u-font-medium    { font-weight: var(--font-medium); }
.u-font-semibold  { font-weight: var(--font-semibold); }
.u-font-bold      { font-weight: var(--font-bold); }

.u-text-primary   { color: var(--color-text-primary); }
.u-text-secondary { color: var(--color-text-secondary); }
.u-text-tertiary  { color: var(--color-text-tertiary); }
.u-text-muted     { color: var(--color-text-muted); }
.u-text-green     { color: var(--color-primary); }
.u-text-white     { color: var(--color-text-inverse); }

.u-text-center  { text-align: center; }
.u-text-left    { text-align: left; }
.u-text-right   { text-align: right; }

.u-font-mono { font-family: var(--font-mono); }

.u-truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.u-line-clamp-2 {
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.u-line-clamp-3 {
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* --- Spacing --- */
.u-mt-0  { margin-top: 0; }
.u-mt-2  { margin-top: var(--space-2); }
.u-mt-4  { margin-top: var(--space-4); }
.u-mt-6  { margin-top: var(--space-6); }
.u-mt-8  { margin-top: var(--space-8); }

.u-mb-0  { margin-bottom: 0; }
.u-mb-2  { margin-bottom: var(--space-2); }
.u-mb-4  { margin-bottom: var(--space-4); }
.u-mb-6  { margin-bottom: var(--space-6); }
.u-mb-8  { margin-bottom: var(--space-8); }

.u-mx-auto { margin-left: auto; margin-right: auto; }

.u-p-0  { padding: 0; }
.u-p-2  { padding: var(--space-2); }
.u-p-4  { padding: var(--space-4); }
.u-p-6  { padding: var(--space-6); }
.u-p-8  { padding: var(--space-8); }

.u-px-4 { padding-left: var(--space-4); padding-right: var(--space-4); }
.u-px-6 { padding-left: var(--space-6); padding-right: var(--space-6); }
.u-py-2 { padding-top: var(--space-2); padding-bottom: var(--space-2); }
.u-py-4 { padding-top: var(--space-4); padding-bottom: var(--space-4); }

/* --- Backgrounds --- */
.u-bg-white  { background-color: var(--color-bg-white); }
.u-bg-page   { background-color: var(--color-bg-page); }
.u-bg-code   { background-color: var(--color-bg-code); }
.u-bg-green  { background-color: var(--color-primary); }
.u-bg-accent { background-color: var(--color-accent); }

/* --- Borders --- */
.u-border       { border: 1px solid var(--color-border-light); }
.u-border-heavy { border: 1px solid var(--color-border-heavy); }
.u-border-b     { border-bottom: 1px solid var(--color-border-light); }
.u-border-t     { border-top: 1px solid var(--color-border-light); }

.u-rounded-sm   { border-radius: var(--radius-sm); }
.u-rounded-md   { border-radius: var(--radius-md); }
.u-rounded-lg   { border-radius: var(--radius-lg); }
.u-rounded-pill { border-radius: var(--radius-pill); }
.u-rounded-full { border-radius: 9999px; }

/* --- Shadows --- */
.u-shadow-sm { box-shadow: var(--shadow-sm); }
.u-shadow-md { box-shadow: var(--shadow-md); }
.u-shadow-lg { box-shadow: var(--shadow-lg); }

/* --- Sizing --- */
.u-w-full   { width: 100%; }
.u-max-w-md { max-width: 640px; }
.u-max-w-lg { max-width: var(--content-max-width); }
.u-max-w-xl { max-width: 1200px; }

/* --- Overflow --- */
.u-overflow-hidden { overflow: hidden; }
.u-overflow-x-auto { overflow-x: auto; }

/* --- Cursor --- */
.u-cursor-pointer   { cursor: pointer; }
.u-cursor-not-allowed { cursor: not-allowed; }

/* --- Transitions --- */
.u-transition {
  transition-property: color, background-color, border-color, box-shadow, opacity;
  transition-duration: 200ms;
  transition-timing-function: ease;
}

/* --- Visibility / Screen-reader only --- */
.u-sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}


/* ==========================================================================
   Page-specific Styles
   ========================================================================== */

/* --- Hero Section --- */
.hero {
  background-color: var(--color-primary);
  padding: 80px 24px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.hero__inner {
  max-width: 720px;
  margin: 0 auto;
  text-align: center;
}

.hero__title {
  font-size: 40px;
  font-weight: var(--font-bold);
  color: var(--color-text-inverse);
  margin-bottom: var(--space-4);
  line-height: 1.2;
}

.hero__subtitle {
  font-size: var(--text-base);
  color: var(--color-text-inverse);
  opacity: 0.9;
  margin-bottom: var(--space-8);
  line-height: 1.6;
}

.hero__cta {
  background: white;
  color: var(--color-primary);
  font-weight: var(--font-bold);
  font-size: var(--text-base);
  padding: var(--space-3) var(--space-8);
  border-radius: var(--radius-pill);
}

.hero__cta:hover {
  color: var(--color-primary-hover);
  box-shadow: var(--shadow-md);
}

/* --- Section wrappers --- */
.section {
  padding: 64px 24px;
}

.section--white {
  background-color: var(--color-bg-white);
}

.section--gray {
  background-color: var(--color-bg-code);
}

.section--green {
  background-color: var(--color-primary);
}

.section__inner {
  max-width: 1100px;
  margin: 0 auto;
}

.section__inner--narrow {
  max-width: 800px;
}

.section__title {
  font-size: 32px;
  font-weight: var(--font-bold);
  text-align: center;
  margin-bottom: var(--space-10);
  color: var(--color-text-primary);
}

/* --- Programs grid --- */
.programs-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--space-6);
}

/* --- Feature cards (Why CrackCode section) --- */
.features-grid {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 40px;
}

.feature-item {
  flex: 1 1 200px;
  max-width: 220px;
  text-align: center;
}

.feature-item__icon {
  margin: 0 auto var(--space-3);
}

.feature-item__title {
  font-size: var(--text-lg);
  font-weight: var(--font-bold);
  color: var(--color-text-primary);
  margin-bottom: var(--space-2);
}

.feature-item__desc {
  font-size: var(--text-sm);
  color: var(--color-text-tertiary);
  line-height: 1.6;
}

/* --- CTA section --- */
.cta-section {
  background-color: var(--color-primary);
  padding: 64px 24px;
  text-align: center;
}

.cta-section__title {
  font-size: 28px;
  font-weight: var(--font-bold);
  color: var(--color-text-inverse);
  margin-bottom: var(--space-5);
}

/* --- Auth form container --- */
.auth-section {
  padding: 0 var(--space-6);
}

.auth-card {
  background: white;
  border: 1px solid var(--color-border-heavy);
  border-radius: var(--radius-lg);
  padding: var(--space-10) var(--space-10);
  max-width: 420px;
  margin: var(--space-16) auto;
}

.auth-card__title {
  font-size: 28px;
  font-weight: var(--font-bold);
  color: var(--color-text-primary);
  margin: 0 0 var(--space-2);
}

.auth-card__subtitle {
  font-size: var(--text-sm);
  color: var(--color-text-tertiary);
  margin: 0 0 28px;
}

.auth-social-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  width: 100%;
  padding: var(--space-3) var(--space-4);
  background: white;
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
  text-decoration: none;
  cursor: pointer;
  transition: border-color var(--transition-base);
}

.auth-social-btn:hover {
  border-color: var(--color-border-medium);
  color: var(--color-text-primary);
}

.auth-divider {
  position: relative;
  text-align: center;
  margin: var(--space-6) 0;
}

.auth-divider__line {
  border-top: 1px solid var(--color-border-light);
}

.auth-divider__text {
  position: absolute;
  top: -10px;
  left: 50%;
  transform: translateX(-50%);
  background: white;
  padding: 0 var(--space-3);
  font-size: 13px;
  color: var(--color-text-muted);
}

.auth-form {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.auth-input {
  width: 100%;
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-family: inherit;
  outline: none;
  transition: border-color var(--transition-base);
  box-sizing: border-box;
}

.auth-input:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(20, 159, 118, 0.1);
}

.auth-error {
  color: #EF4444;
  font-size: var(--text-sm);
  margin-top: var(--space-3);
}

.auth-footer {
  font-size: var(--text-sm);
  color: var(--color-text-tertiary);
  text-align: center;
  margin-top: var(--space-6);
}

.auth-footer a {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: var(--font-semibold);
}

/* --- Day page header --- */
.day-header {
  margin-bottom: var(--space-8);
}

.day-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}

.day-tag {
  display: inline-flex;
  align-items: center;
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  line-height: 1;
  padding: 4px 10px;
  border-radius: var(--radius-pill);
}

.day-title {
  font-size: 32px;
  font-weight: var(--font-bold);
  color: var(--color-text-primary);
  margin-bottom: var(--space-2);
  line-height: 1.25;
}

.day-description {
  font-size: var(--text-base);
  color: var(--color-text-tertiary);
  line-height: 1.6;
  margin-bottom: var(--space-2);
}

.day-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-4);
  margin-top: var(--space-2);
}

.day-meta__item {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  margin: 0;
}

.day-meta__link {
  font-size: 13px;
  font-weight: var(--font-semibold);
  color: var(--color-primary);
}

/* --- Mark complete button --- */
.complete-btn-wrapper {
  margin-top: var(--space-8);
  display: flex;
  justify-content: center;
}

.complete-btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) 28px;
  border-radius: var(--radius-pill);
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  cursor: pointer;
  transition: all var(--transition-base);
  font-family: inherit;
}

/* --- Day navigation footer --- */
.day-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: var(--space-12);
  padding-top: var(--space-6);
  border-top: 1px solid var(--color-border-light);
}

/* --- Card header with icon --- */
.card__header--with-icon {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

/* --- Card status text --- */
.card__status {
  margin-top: var(--space-3);
  font-size: 13px;
  font-weight: var(--font-semibold);
}

.card__status--active {
  color: var(--color-primary);
}

.card__status--muted {
  color: var(--color-text-muted);
}

/* --- Program detail course outline items --- */
.outline-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  margin-bottom: var(--space-10);
}

.outline-item {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-4) var(--space-5);
}

.outline-item__number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  min-width: 36px;
  border-radius: 50%;
  background-color: var(--color-accent);
  color: var(--color-text-inverse);
  font-size: var(--text-sm);
  font-weight: var(--font-bold);
}

.outline-item__title {
  font-size: 15px;
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
}


/* ==========================================================================
   Collapsible Phase Sections
   ========================================================================== */

.phase-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
}

.phase-toggle-all {
  background: none;
  border-width: 1px !important;
  border-style: solid !important;
  border-color: var(--color-border) !important;
  border-radius: 6px;
  padding: 6px 14px;
  font-size: 13px;
  color: var(--color-text-secondary);
  cursor: pointer;
  font-family: inherit;
  transition: color 0.15s, border-color 0.15s;
}

.phase-toggle-all:hover {
  color: var(--color-accent);
  border-color: var(--color-accent) !important;
}

.phase-progress-bar {
  height: 6px;
  background-color: var(--color-bg-secondary) !important;
  border-radius: 3px;
  overflow: hidden;
}

.phase-progress-bar__fill {
  height: 100%;
  background: var(--color-accent);
  border-radius: 3px;
  transition: width 0.3s ease;
}

.phase-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.phase-group {
  border-width: 1px !important;
  border-style: solid !important;
  border-color: var(--color-border) !important;
  border-radius: 8px;
  overflow: hidden;
  background-color: var(--color-bg-primary) !important;
}

.phase-group[open] {
  border-color: var(--color-accent) !important;
}

.phase-group[open] > .phase-summary {
  border-bottom-width: 1px !important;
  border-bottom-style: solid !important;
  border-bottom-color: var(--color-border) !important;
}

summary.phase-summary {
  display: flex !important;
  align-items: center;
  justify-content: space-between;
  padding: 14px 16px;
  cursor: pointer;
  list-style: none;
  user-select: none;
  transition: background 0.15s;
}

summary.phase-summary::-webkit-details-marker {
  display: none;
}

summary.phase-summary::marker {
  display: none;
  content: "";
}

.phase-summary:hover {
  background: var(--color-bg-secondary);
}

.phase-summary__left {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
}

.phase-summary__chevron {
  display: flex;
  align-items: center;
  color: var(--color-text-tertiary);
  transition: transform 0.2s ease;
  flex-shrink: 0;
}

.phase-group[open] > .phase-summary .phase-summary__chevron {
  transform: rotate(90deg);
}

.phase-summary__number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  min-width: 28px;
  border-radius: 50%;
  background: var(--color-accent);
  color: var(--color-text-inverse);
  font-size: 12px;
  font-weight: var(--font-bold);
}

.phase-summary__info {
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: 0;
}

.phase-summary__name {
  font-size: 15px;
  font-weight: var(--font-semibold);
  color: var(--color-text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.phase-summary__range {
  font-size: 12px;
  color: var(--color-text-tertiary);
}

.phase-summary__right {
  flex-shrink: 0;
  margin-left: 12px;
}

.phase-badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 12px;
  font-weight: var(--font-semibold);
  color: var(--color-text-tertiary);
  background-color: var(--color-bg-secondary) !important;
  padding: 4px 10px;
  border-radius: 12px;
}

.phase-badge--done {
  color: var(--color-accent);
  background-color: rgba(20, 159, 118, 0.1) !important;
}

.phase-days {
  display: flex !important;
  flex-direction: column;
}

.phase-day-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px 12px 56px;
  text-decoration: none;
  color: inherit;
  border-bottom-width: 1px !important;
  border-bottom-style: solid !important;
  border-bottom-color: var(--color-border) !important;
  transition: background 0.15s;
}

.phase-day-card:last-child {
  border-bottom-width: 0 !important;
  border-bottom-style: none !important;
}

.phase-day-card:hover {
  background: var(--color-bg-secondary);
}

.phase-day-card--done {
  opacity: 0.7;
}

.phase-day-card__number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  min-width: 28px;
  border-radius: 50%;
  background-color: var(--color-bg-secondary) !important;
  color: var(--color-text-secondary);
  font-size: 12px;
  font-weight: var(--font-semibold);
}

.phase-day-card--done .phase-day-card__number {
  background-color: rgba(20, 159, 118, 0.1) !important;
  color: var(--color-accent);
}

.phase-day-card__title {
  font-size: 14px;
  color: var(--color-text-primary);
  flex: 1;
  min-width: 0;
}

.phase-day-card__check {
  color: var(--color-accent);
  flex-shrink: 0;
}

@media (max-width: 480px) {
  .phase-summary {
    padding: 12px;
  }

  .phase-day-card {
    padding: 10px 12px 10px 40px;
  }

  .phase-summary__name {
    font-size: 13px;
  }

  .phase-header {
    flex-wrap: wrap;
    gap: 8px;
  }
}


/* ==========================================================================
   11. Mobile Navigation Drawer
   ========================================================================== */

.mobile-nav {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  background-color: var(--color-bg-white);
  border-bottom: 1px solid var(--color-border-light);
  box-shadow: var(--shadow-md);
  padding: var(--space-2) 0;
  flex-direction: column;
  z-index: 999;
}

.mobile-nav--open {
  display: flex;
}

.mobile-nav__link {
  display: block;
  padding: var(--space-3) var(--space-6);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--color-text-secondary);
  text-decoration: none;
  transition: background-color var(--transition-fast);
}

.mobile-nav__link:hover {
  background-color: var(--color-bg-page);
  color: var(--color-primary);
}

.mobile-nav__link--muted {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.mobile-nav__link--cta {
  color: var(--color-primary);
  font-weight: var(--font-bold);
}

/* ==========================================================================
   Responsive Overrides
   ========================================================================== */

@media (max-width: 1024px) {
  .site-header__menu-toggle {
    display: flex;
  }

  .site-header__nav {
    display: none;
  }

  .sidebar {
    transform: translateX(-100%);
    transition: transform var(--transition-slow);
    z-index: 200;
  }

  .sidebar--open {
    transform: translateX(0);
    box-shadow: var(--shadow-lg);
  }

  .sidebar__close {
    display: flex;
  }

  .main-content {
    margin-left: 0;
  }
}

@media (max-width: 768px) {
  :root {
    --header-height: 56px;
  }

  .main-content {
    padding: var(--space-6) var(--space-4);
  }

  .lesson-content h1 {
    font-size: var(--text-xl);
  }

  .lesson-content h2 {
    font-size: var(--text-lg);
  }

  .site-footer__inner {
    grid-template-columns: 1fr;
    gap: var(--space-6);
  }

  .card {
    border-radius: var(--radius-md);
  }

  /* Hero responsive */
  .hero {
    padding: 48px 16px;
  }

  .hero__title {
    font-size: 28px;
  }

  .hero__subtitle {
    font-size: var(--text-sm);
  }

  /* Section responsive */
  .section {
    padding: 40px 16px;
  }

  .section__title {
    font-size: 24px;
    margin-bottom: var(--space-6);
  }

  /* Features responsive */
  .features-grid {
    gap: 24px;
  }

  .feature-item {
    flex: 1 1 140px;
    max-width: 180px;
  }

  .feature-item__title {
    font-size: var(--text-base);
  }

  /* CTA responsive */
  .cta-section {
    padding: 40px 16px;
  }

  .cta-section__title {
    font-size: 22px;
  }

  /* Auth responsive */
  .auth-card {
    padding: var(--space-6);
    margin: var(--space-8) auto;
    border-radius: var(--radius-md);
  }

  .auth-card__title {
    font-size: 24px;
  }

  /* Day page responsive */
  .day-title {
    font-size: 24px;
  }

  .day-meta {
    gap: var(--space-2);
  }

  .day-nav {
    flex-direction: column;
    gap: var(--space-3);
  }

  .day-nav .btn {
    width: 100%;
    justify-content: center;
  }

  /* Programs grid responsive */
  .programs-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .hero__title {
    font-size: 24px;
  }

  .features-grid {
    flex-direction: column;
    align-items: center;
  }

  .feature-item {
    max-width: 280px;
  }

  .auth-section {
    padding: 0 var(--space-3);
  }

  .auth-card {
    padding: var(--space-5);
  }
}

/* ===========================
   13. Explain Simply Blocks
   =========================== */

details.eli-simple {
  margin: 8px 0 12px 0;
}

details.eli-simple > summary {
  font-size: 0.85rem;
  color: var(--color-text-tertiary);
  cursor: pointer;
  list-style: none;
  user-select: none;
  transition: color 0.15s ease;
}

details.eli-simple > summary::-webkit-details-marker {
  display: none;
}

details.eli-simple > summary::before {
  content: "▸ ";
}

details.eli-simple[open] > summary {
  color: var(--color-text-secondary);
}

details.eli-simple[open] > summary::before {
  content: "▾ ";
}

details.eli-simple > div {
  margin-top: 6px;
  padding: 12px 16px;
  background-color: var(--color-bg-code);
  border-left-width: 2px !important;
  border-left-style: solid !important;
  border-left-color: #149F76 !important;
  border-radius: 0 4px 4px 0;
  font-size: 0.9rem;
  line-height: 1.6;
  color: var(--color-text-secondary);
}

details.eli-simple > div p {
  margin: 0 0 8px 0;
}

details.eli-simple > div p:last-child {
  margin-bottom: 0;
}