/* ==========================================================================
   Base: reset, typography, app shell (topbar + sidebar + content)
   ========================================================================== */

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--topbar-h) + 16px);
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: var(--fs-md);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

/* Ambient background glow */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background:
    radial-gradient(800px 520px at 85% -10%, color-mix(in srgb, var(--mod) 24%, transparent), transparent 70%),
    radial-gradient(700px 520px at -10% 35%, color-mix(in srgb, var(--mod-2) 14%, transparent), transparent 70%),
    radial-gradient(600px 420px at 60% 110%, rgba(244, 114, 182, 0.1), transparent 70%);
}

/* Neon grid floor */
body::after {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
  background-size: 44px 44px;
  mask-image: radial-gradient(ellipse at 50% 0%, #000 20%, transparent 75%);
  -webkit-mask-image: radial-gradient(ellipse at 50% 0%, #000 20%, transparent 75%);
}

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

h1,
h2,
h3,
h4 {
  font-family: var(--font-display);
  line-height: 1.2;
  letter-spacing: -0.02em;
  margin: 0 0 var(--sp-3);
}

h2 {
  font-size: var(--fs-xl);
}
h3 {
  font-size: var(--fs-lg);
}

p {
  margin: 0 0 var(--sp-4);
}

a {
  color: inherit;
}

.content a:not([class]) {
  color: var(--mod);
  text-decoration: underline;
  text-decoration-color: color-mix(in srgb, var(--mod) 40%, transparent);
  text-underline-offset: 3px;
}
.content a:not([class]):hover {
  text-decoration-color: currentColor;
}

ul,
ol {
  padding-left: 1.3em;
  margin: 0 0 var(--sp-4);
}
li + li {
  margin-top: 6px;
}

strong {
  font-weight: 600;
  color: var(--text);
}

:focus-visible {
  outline: 2px solid var(--mod);
  outline-offset: 3px;
  border-radius: 6px;
}

::selection {
  background: color-mix(in srgb, var(--mod) 35%, transparent);
}

button {
  font: inherit;
  color: inherit;
  cursor: pointer;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

/* --------------------------------------------------------------------------
   Topbar
   -------------------------------------------------------------------------- */

.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  height: var(--topbar-h);
  z-index: 50;
  display: flex;
  align-items: center;
  gap: var(--sp-4);
  padding: 0 var(--sp-5);
  background: color-mix(in srgb, var(--bg) 78%, transparent);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  border-bottom: 1px solid var(--border);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.08rem;
  letter-spacing: -0.02em;
  white-space: nowrap;
}

.brand-mark {
  width: 36px;
  height: 36px;
  flex: none;
  border-radius: 11px;
  box-shadow: 0 0 20px -4px color-mix(in srgb, var(--brand) 75%, transparent);
  transition: transform 0.4s var(--ease);
}
.brand:hover .brand-mark {
  transform: rotate(-8deg) scale(1.06);
}

.brand small {
  color: var(--text-faint);
  font-weight: 500;
  margin-left: 2px;
}

.crumbs {
  display: flex;
  align-items: center;
  gap: 8px;
  min-width: 0;
  font-size: var(--fs-sm);
  color: var(--text-muted);
}
.crumbs a {
  text-decoration: none;
  white-space: nowrap;
}
.crumbs a:hover {
  color: var(--text);
}
.crumbs .sep {
  color: var(--text-faint);
}
.crumbs .current {
  color: var(--text);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.topbar-spacer {
  flex: 1;
}

.icon-btn {
  width: 40px;
  height: 40px;
  flex: none;
  display: grid;
  place-items: center;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  transition: transform 0.2s var(--ease), border-color 0.2s;
}
.icon-btn:hover {
  border-color: var(--border-strong);
  transform: translateY(-1px);
}
.icon-btn svg {
  width: 19px;
  height: 19px;
}

.theme-toggle .sun {
  display: none;
}
:root[data-theme="light"] .theme-toggle .sun {
  display: block;
}
:root[data-theme="light"] .theme-toggle .moon {
  display: none;
}

.menu-btn {
  display: none;
}

/* --------------------------------------------------------------------------
   Sidebar
   -------------------------------------------------------------------------- */

.sidebar {
  position: fixed;
  top: var(--topbar-h);
  bottom: 0;
  left: 0;
  width: var(--sidebar-w);
  z-index: 40;
  overflow-y: auto;
  padding: var(--sp-5) var(--sp-4) var(--sp-7);
  border-right: 1px solid var(--border);
  background: color-mix(in srgb, var(--bg) 92%, transparent);
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.side-label {
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-faint);
  font-weight: 600;
  margin: 0 var(--sp-2) var(--sp-3);
}

.side-module {
  margin-bottom: 4px;
}

.side-module > summary {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 10px;
  border-radius: 10px;
  cursor: pointer;
  font-size: var(--fs-sm);
  font-weight: 500;
  color: var(--text-muted);
  transition: background 0.15s, color 0.15s;
}
.side-module > summary::-webkit-details-marker {
  display: none;
}
.side-module > summary:hover {
  background: var(--surface);
  color: var(--text);
}
.side-module[open] > summary {
  color: var(--text);
}

.side-num {
  flex: none;
  width: 26px;
  height: 26px;
  border-radius: 8px;
  display: grid;
  place-items: center;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  color: #fff;
  background: linear-gradient(135deg, var(--c1), var(--c2));
}

.side-title {
  flex: 1;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.side-chev {
  width: 14px;
  height: 14px;
  color: var(--text-faint);
  transition: transform 0.2s var(--ease);
}
.side-module[open] .side-chev {
  transform: rotate(90deg);
}

.side-lessons {
  list-style: none;
  margin: 4px 0 10px 22px;
  padding: 0 0 0 14px;
  border-left: 1px dashed var(--border-strong);
}
.side-lessons li {
  margin: 0;
}
.side-lessons a {
  display: block;
  padding: 6px 10px;
  border-radius: 8px;
  text-decoration: none;
  font-size: 0.86rem;
  color: var(--text-muted);
  line-height: 1.35;
  transition: background 0.15s, color 0.15s;
}
.side-lessons a:hover {
  color: var(--text);
  background: var(--surface);
}
.side-lessons a[aria-current="page"] {
  color: var(--text);
  font-weight: 600;
  background: color-mix(in srgb, var(--c1) 16%, transparent);
  box-shadow: inset 3px 0 0 var(--c1);
}

.scrim {
  display: none;
}

/* --------------------------------------------------------------------------
   Content area
   -------------------------------------------------------------------------- */

.shell {
  padding-top: var(--topbar-h);
}

body.has-sidebar .shell {
  padding-left: var(--sidebar-w);
}

.content {
  width: 100%;
  max-width: calc(var(--content-w) + 2 * var(--sp-6));
  margin: 0 auto;
  padding: var(--sp-6) var(--sp-6) var(--sp-8);
}

.site-footer {
  border-top: 1px solid var(--border);
  padding: var(--sp-6) var(--sp-5);
  text-align: center;
  color: var(--text-faint);
  font-size: var(--fs-sm);
}

/* --------------------------------------------------------------------------
   Reveal-on-scroll (only when JS has opted in)
   -------------------------------------------------------------------------- */

.js-reveal .reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.7s var(--ease), transform 0.7s var(--ease);
}
.js-reveal .reveal.is-visible {
  opacity: 1;
  transform: none;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
  .js-reveal .reveal {
    opacity: 1;
    transform: none;
  }
}

/* --------------------------------------------------------------------------
   Responsive
   -------------------------------------------------------------------------- */

@media (max-width: 1100px) {
  .crumbs .crumb-module {
    display: none;
  }
}

@media (max-width: 900px) {
  .menu-btn {
    display: grid;
  }
  .sidebar {
    transform: translateX(-105%);
    transition: transform 0.3s var(--ease);
    width: min(86vw, 320px);
    background: var(--bg);
    box-shadow: var(--shadow-lg);
  }
  body.nav-open .sidebar {
    transform: none;
  }
  body.nav-open .scrim {
    display: block;
    position: fixed;
    inset: var(--topbar-h) 0 0 0;
    z-index: 35;
    background: rgba(5, 7, 15, 0.55);
    backdrop-filter: blur(2px);
  }
  body.has-sidebar .shell {
    padding-left: 0;
  }
  .crumbs {
    display: none;
  }
}

@media (max-width: 640px) {
  .topbar {
    padding: 0 var(--sp-4);
    padding-left: max(var(--sp-4), env(safe-area-inset-left));
    padding-right: max(var(--sp-4), env(safe-area-inset-right));
    gap: var(--sp-3);
  }
  .brand small {
    display: none;
  }
  .content {
    padding: var(--sp-5) var(--sp-4) var(--sp-7);
  }
}

/* Notched phones: keep content clear of the rounded corners */
.content {
  padding-left: max(var(--sp-6), env(safe-area-inset-left));
  padding-right: max(var(--sp-6), env(safe-area-inset-right));
}

@media (max-width: 640px) {
  .content {
    padding-left: max(var(--sp-4), env(safe-area-inset-left));
    padding-right: max(var(--sp-4), env(safe-area-inset-right));
  }
}

@media (max-width: 400px) {
  :root {
    --topbar-h: 58px;
  }
  .topbar {
    gap: 8px;
    padding: 0 12px;
  }
  .brand {
    gap: 8px;
    font-size: 0.98rem;
    min-width: 0;
  }
  .brand-name {
    overflow: hidden;
    text-overflow: ellipsis;
  }
  .brand-mark {
    width: 32px;
    height: 32px;
  }
  .icon-btn {
    width: 38px;
    height: 38px;
  }
}

@media (max-width: 340px) {
  .brand-name {
    display: none;
  }
}

/* Footer respects the iPhone home indicator */
.site-footer {
  padding-bottom: max(var(--sp-6), env(safe-area-inset-bottom));
}

/* Tap targets: never smaller than 40px on touch screens */
@media (pointer: coarse) {
  .side-lessons a {
    padding-top: 9px;
    padding-bottom: 9px;
  }
  .side-module > summary {
    padding-top: 10px;
    padding-bottom: 10px;
  }
}