@import url('https://fonts.googleapis.com/css2?family=Montserrat:wght@300;400;500&display=swap');

/* ─── CSS Variables ─────────────────────────────────────────── */
:root {
  --color-bg:        #ffffff;
  --color-surface:   #f8f8f6;
  --color-border:    #e0ddd8;
  --color-text:      #1a1e2d;
  --color-text-muted:#5a5f72;
  --color-accent:    #3a6498;
  --color-accent-hover: #2a4f7e;
  --color-sidebar-bg:#f5f4f1;
  --header-height:   64px;
  --sidebar-width:   240px;
  --font-display:    'Montserrat', sans-serif;
  --font-body:       'Montserrat', sans-serif;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  font-weight: 300;
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

/* ─── Links ─────────────────────────────────────────────────── */
a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color 0.2s ease;
}

a:hover,
a:focus {
  color: var(--color-accent-hover);
  text-decoration: underline;
  text-underline-offset: 3px;
}

/* ─── Header ────────────────────────────────────────────────── */
.site-header {
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  padding: 0 2rem;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  z-index: 100;
  gap: 1rem;
}

.site-title {
  font-family: var(--font-display);
  font-weight: 400;
  font-size: 1.35rem;
  letter-spacing: 0.35em;
  color: var(--color-text);
  text-decoration: none;
  text-transform: uppercase;
  flex: 1;
  transition: opacity 0.2s ease;
}

.site-title:hover {
  opacity: 0.7;
  text-decoration: none;
  color: var(--color-text);
}

/* ─── Menu Button ───────────────────────────────────────────── */
.menu-btn {
  background: none;
  border: none;
  color: var(--color-text);
  cursor: pointer;
  font-size: 1.4rem;
  padding: 0.25rem;
  display: flex;
  align-items: center;
  opacity: 0.75;
  transition: opacity 0.2s ease;
  order: -1;
}

.menu-btn:hover {
  opacity: 1;
}

/* ─── Search ────────────────────────────────────────────────── */
.search-wrapper {
  position: relative;
}

.search-wrapper input[type="search"] {
  padding: 0.35rem 2.25rem 0.35rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: 20px;
  background: var(--color-surface);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: 0.85rem;
  font-weight: 300;
  outline: none;
  transition: border-color 0.2s ease, background 0.2s ease;
  width: 180px;
}

.search-wrapper input[type="search"]:focus {
  border-color: var(--color-accent);
  background: var(--color-bg);
}

.search-icon {
  position: absolute;
  right: 0.6rem;
  top: 50%;
  transform: translateY(-50%);
  pointer-events: none;
  font-size: 1rem;
  color: var(--color-text-muted);
}

/* ─── GitHub Link ───────────────────────────────────────────── */
.github-link {
  color: var(--color-text);
  text-decoration: none;
  display: flex;
  align-items: center;
  opacity: 0.65;
  transition: opacity 0.2s ease;
}

.github-link:hover {
  opacity: 1;
  text-decoration: none;
}

.github-icon {
  width: 28px;
  height: auto;
  display: inline-block;
  vertical-align: middle;
  filter: grayscale(100%);
}

/* ─── Layout ────────────────────────────────────────────────── */
.layout {
  display: flex;
  height: calc(100vh - var(--header-height));
  margin-top: var(--header-height);
  overflow: hidden;
}

/* ─── Sidebar ───────────────────────────────────────────────── */
.sidebar {
  flex: 0 0 var(--sidebar-width);
  background: var(--color-sidebar-bg);
  border-right: 1px solid var(--color-border);
  padding: 2.5rem 1.5rem;
  overflow-y: auto;
  transition: flex 0.25s ease, padding 0.25s ease;
}

.sidebar.collapsed {
  flex: 0 0 0;
  padding: 0;
  overflow: hidden;
}

.sidebar-title {
  font-family: var(--font-body);
  font-size: 0.68rem;
  font-weight: 500;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  margin-bottom: 1.5rem;
}

.sidebar-list {
  list-style: none;
}

.sidebar-list li {
  border-bottom: 1px solid var(--color-border);
}

.sidebar-list li:first-child {
  border-top: 1px solid var(--color-border);
}

.sidebar-list a {
  display: block;
  padding: 0.7rem 0;
  font-size: 0.82rem;
  font-weight: 300;
  color: var(--color-text);
  text-decoration: none;
  line-height: 1.45;
  transition: color 0.15s ease, padding-left 0.15s ease;
}

.sidebar-list a:hover {
  color: var(--color-accent);
  padding-left: 0.4rem;
  text-decoration: none;
}

/* ─── Main Content ──────────────────────────────────────────── */
.content {
  flex: 1 1 auto;
  min-width: 0;
  overflow-y: auto;
  padding: 3.5rem 4rem 4rem 3.5rem;
}

.content h1 {
  font-family: var(--font-display);
  font-size: 2.4rem;
  font-weight: 300;
  letter-spacing: 0.06em;
  color: var(--color-text);
  margin-bottom: 0.75rem;
  line-height: 1.2;
}

.content h2 {
  font-family: var(--font-body);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  margin-bottom: 1rem;
}

.content p {
  font-size: 0.95rem;
  color: var(--color-text-muted);
  margin-bottom: 2.5rem;
  max-width: 560px;
}

/* ─── Tutorial List ─────────────────────────────────────────── */
.tutorial-list {
  list-style: none;
  max-width: 680px;
}

.tutorial-list > li {
  border-top: 1px solid var(--color-border);
  padding: 1.1rem 0;
}

.tutorial-list > li:last-child {
  border-bottom: 1px solid var(--color-border);
}

.tutorial-list > li > a {
  font-size: 0.93rem;
  font-weight: 400;
  color: var(--color-text);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  transition: color 0.15s ease;
}

.tutorial-list > li > a::before {
  content: '';
  display: inline-block;
  width: 18px;
  height: 1px;
  background: var(--color-border);
  flex-shrink: 0;
  transition: width 0.2s ease, background 0.2s ease;
}

.tutorial-list > li > a:hover {
  color: var(--color-accent);
  text-decoration: none;
}

.tutorial-list > li > a:hover::before {
  width: 28px;
  background: var(--color-accent);
}

/* Subchapters */
.tutorial-list .subchapters {
  list-style: none;
  margin: 0.6rem 0 0 2.5rem;
  padding: 0;
}

.tutorial-list .subchapters li {
  padding: 0.3rem 0;
}

.tutorial-list .subchapters a {
  font-size: 0.82rem;
  font-weight: 300;
  color: var(--color-text-muted);
}

.tutorial-list .subchapters a:hover {
  color: var(--color-accent);
}

/* ─── Chapter Sections ──────────────────────────────────────── */
.chapter {
  margin-top: 2.5rem;
  margin-bottom: 3.5rem;
}

.chapter h1 {
  font-family: var(--font-display);
  font-size: 1.6rem;
  font-weight: 300;
  letter-spacing: 0.04em;
  margin-bottom: 1.5rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--color-border);
}

/* ─── Responsive ────────────────────────────────────────────── */
@media (max-width: 800px) {
  .site-header {
    padding: 0 1rem;
  }

  .search-wrapper input[type="search"] {
    width: 130px;
  }

  .content {
    padding: 2rem 1.5rem;
    flex: 1 1 100%;
  }

  .content h1 {
    font-size: 1.8rem;
  }

  /* Hide sidebar by default on mobile */
  .sidebar {
    position: fixed;
    top: var(--header-height);
    left: 0;
    bottom: 0;
    z-index: 99;
    width: var(--sidebar-width);
    flex: none;
    padding: 2rem 1.5rem;
    box-shadow: 4px 0 20px rgba(0,0,0,0.08);
    transform: translateX(-100%);
    transition: transform 0.25s ease;
  }

  /* Show sidebar only when .open is added */
  .sidebar.open {
    transform: translateX(0);
  }

  /* Collapsed class does nothing extra on mobile — open/close handles it */
  .sidebar.collapsed {
    transform: translateX(-100%);
  }

  .chapter {
    padding-right: 0;
  }
}