/* ── Variables ─────────────────────────────────────────────────────────────── */
:root {
  --primary:       #149ddd;
  --primary-dark:  #0f7db5;
  --sidebar-bg:    #040b14;
  --sidebar-text:  #a8b2c1;
  --sidebar-hover: #1a2a3a;
  --sidebar-w:     280px;
  --easy:          #22c55e;
  --medium:        #f59e0b;
  --hard:          #ef4444;
  --unknown:       #94a3b8;
  --card-bg:       #ffffff;
  --card-border:   #e5e7eb;
  --card-hover:    #f0f9ff;
  --body-bg:       #f5f8fd;
  --text:          #374151;
  --text-muted:    #6b7280;
  --heading:       #111827;
  --section-alt:   #f9fafb;
  --radius:        8px;
  --shadow:        0 1px 4px rgba(0,0,0,.08);
  --shadow-hover:  0 4px 16px rgba(20,157,221,.18);
  --transition:    .2s ease;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: 'Open Sans', sans-serif;
  background: var(--body-bg);
  color: var(--text);
  line-height: 1.6;
  display: flex;
  min-height: 100vh;
}

a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--primary-dark); }

ul { list-style: none; }

/* ── Sidebar ───────────────────────────────────────────────────────────────── */
#sidebar {
  position: fixed;
  top: 0; left: 0;
  width: var(--sidebar-w);
  height: 100vh;
  background: var(--sidebar-bg);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  z-index: 100;
  transition: transform var(--transition);
}

.sidebar-inner {
  padding: 28px 20px 40px;
  flex: 1;
}

/* ── Sidebar — logo / branding ─────────────────────────────────────────────── */
.sidebar-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 28px;
  padding-bottom: 20px;
  border-bottom: 1px solid rgba(255,255,255,.07);
}

.brand-icon {
  width: 44px; height: 44px;
  background: var(--primary);
  border-radius: var(--radius);
  display: flex; align-items: center; justify-content: center;
  font-size: 22px; color: #fff; flex-shrink: 0;
}

.brand-text h1 {
  font-family: 'Raleway', sans-serif;
  font-size: 17px; font-weight: 700;
  color: #fff; line-height: 1.2;
}

.brand-text span {
  font-size: 11px;
  color: var(--sidebar-text);
}

/* ── Sidebar — stats ───────────────────────────────────────────────────────── */
.stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin-bottom: 24px;
}

.stat-item {
  background: rgba(255,255,255,.05);
  border-radius: var(--radius);
  padding: 10px 12px;
  text-align: center;
  cursor: pointer;
  border: 1px solid transparent;
  transition: border-color var(--transition), background var(--transition);
}

.stat-item:hover,
.stat-item.active {
  border-color: var(--primary);
  background: rgba(20,157,221,.12);
}

.stat-item.all .stat-num  { color: var(--primary); }
.stat-item.easy .stat-num { color: var(--easy); }
.stat-item.medium .stat-num { color: var(--medium); }
.stat-item.hard .stat-num { color: var(--hard); }

.stat-num {
  font-family: 'Raleway', sans-serif;
  font-size: 22px; font-weight: 800;
  display: block; line-height: 1;
}

.stat-label {
  font-size: 10px; font-weight: 600;
  color: var(--sidebar-text);
  text-transform: uppercase; letter-spacing: .5px;
}

/* ── Sidebar — search ──────────────────────────────────────────────────────── */
.search-box {
  position: relative;
  margin-bottom: 20px;
}

.search-box i {
  position: absolute;
  left: 11px; top: 50%;
  transform: translateY(-50%);
  color: var(--sidebar-text);
  font-size: 14px;
  pointer-events: none;
}

.search-box input {
  width: 100%;
  padding: 9px 12px 9px 34px;
  background: rgba(255,255,255,.07);
  border: 1px solid rgba(255,255,255,.1);
  border-radius: var(--radius);
  color: #fff;
  font-size: 13px;
  font-family: 'Open Sans', sans-serif;
  transition: border-color var(--transition);
  outline: none;
}

.search-box input::placeholder { color: var(--sidebar-text); }
.search-box input:focus { border-color: var(--primary); }

/* ── Sidebar — categories ──────────────────────────────────────────────────── */
.sidebar-section-title {
  font-size: 10px; font-weight: 700;
  color: rgba(168,178,193,.5);
  text-transform: uppercase; letter-spacing: 1px;
  margin-bottom: 8px;
}

.category-list { display: flex; flex-direction: column; gap: 2px; }

.cat-item {
  display: flex; align-items: center; justify-content: space-between;
  padding: 7px 10px;
  border-radius: 5px;
  cursor: pointer;
  color: var(--sidebar-text);
  font-size: 13px;
  transition: background var(--transition), color var(--transition);
}

.cat-item:hover,
.cat-item.active {
  background: var(--sidebar-hover);
  color: var(--primary);
}

.cat-item .cat-name {
  display: flex; align-items: center; gap: 8px;
}

.cat-item i { font-size: 14px; width: 16px; text-align: center; }

.cat-badge {
  font-size: 11px; font-weight: 600;
  background: rgba(255,255,255,.08);
  padding: 1px 7px; border-radius: 10px;
}

/* ── Sidebar — footer links ────────────────────────────────────────────────── */
.sidebar-footer {
  margin-top: auto;
  padding-top: 20px;
  border-top: 1px solid rgba(255,255,255,.07);
  display: flex; gap: 12px;
}

.sidebar-footer a {
  color: var(--sidebar-text);
  font-size: 18px;
  transition: color var(--transition);
}

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

/* ── Mobile nav toggle ─────────────────────────────────────────────────────── */
.mobile-nav-toggle {
  display: none;
  position: fixed;
  top: 14px; left: 14px;
  z-index: 200;
  width: 40px; height: 40px;
  background: var(--primary);
  color: #fff;
  border: none; border-radius: var(--radius);
  font-size: 20px; cursor: pointer;
  align-items: center; justify-content: center;
}

.sidebar-overlay {
  display: none;
  position: fixed; inset: 0;
  background: rgba(0,0,0,.5);
  z-index: 99;
}

/* ── Main content ──────────────────────────────────────────────────────────── */
#main {
  margin-left: var(--sidebar-w);
  flex: 1;
  min-width: 0;
}

/* ── Top bar ───────────────────────────────────────────────────────────────── */
.topbar {
  background: #fff;
  border-bottom: 1px solid var(--card-border);
  padding: 16px 28px;
  display: flex; align-items: center; justify-content: space-between;
  gap: 12px;
  position: sticky; top: 0; z-index: 50;
}

.topbar-title {
  font-family: 'Raleway', sans-serif;
  font-size: 20px; font-weight: 700;
  color: var(--heading);
}

.topbar-title span { color: var(--primary); }

.sort-select {
  padding: 7px 12px;
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  font-size: 13px;
  font-family: 'Open Sans', sans-serif;
  color: var(--text);
  background: #fff;
  cursor: pointer;
  outline: none;
}

/* ── Problem grid ──────────────────────────────────────────────────────────── */
.grid-container { padding: 24px 28px; }

.results-info {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 16px;
}

.problems-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}

/* ── Problem card ──────────────────────────────────────────────────────────── */
.problem-card {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px 20px;
  display: flex; flex-direction: column; gap: 10px;
  cursor: pointer;
  box-shadow: var(--shadow);
  transition: box-shadow var(--transition), border-color var(--transition),
              background var(--transition), transform var(--transition);
  text-decoration: none; color: inherit;
}

.problem-card:hover {
  box-shadow: var(--shadow-hover);
  border-color: var(--primary);
  background: var(--card-hover);
  transform: translateY(-2px);
}

.card-header {
  display: flex; align-items: center; gap: 8px; flex-wrap: wrap;
}

.diff-badge {
  font-size: 11px; font-weight: 700;
  padding: 3px 9px; border-radius: 12px;
  text-transform: uppercase; letter-spacing: .5px;
  flex-shrink: 0;
}

.diff-badge.easy   { background: rgba(34,197,94,.12);  color: #16a34a; }
.diff-badge.medium { background: rgba(245,158,11,.12); color: #d97706; }
.diff-badge.hard   { background: rgba(239,68,68,.12);  color: #dc2626; }
.diff-badge.unknown{ background: rgba(148,163,184,.12); color: #64748b; }

.problem-num {
  font-size: 12px; font-weight: 600;
  color: var(--text-muted);
}

.card-title {
  font-family: 'Raleway', sans-serif;
  font-size: 15px; font-weight: 700;
  color: var(--heading); line-height: 1.3;
}

.card-category {
  font-size: 12px; color: var(--primary);
  display: flex; align-items: center; gap: 4px;
}

.card-tags {
  display: flex; flex-wrap: wrap; gap: 5px;
}

.tag-chip {
  font-size: 11px;
  background: #f1f5f9;
  color: var(--text-muted);
  padding: 2px 8px; border-radius: 10px;
}

.card-footer {
  display: flex; align-items: center; justify-content: space-between;
  margin-top: auto; padding-top: 8px;
  border-top: 1px solid var(--card-border);
}

.card-date {
  font-size: 11px; color: var(--text-muted);
  display: flex; align-items: center; gap: 4px;
}

.view-link {
  font-size: 12px; font-weight: 600;
  color: var(--primary);
  display: flex; align-items: center; gap: 4px;
  transition: gap var(--transition);
}

.problem-card:hover .view-link { gap: 6px; }

/* ── Empty state ───────────────────────────────────────────────────────────── */
.empty-state {
  grid-column: 1 / -1;
  text-align: center;
  padding: 60px 20px;
  color: var(--text-muted);
}

.empty-state i { font-size: 48px; margin-bottom: 12px; display: block; }
.empty-state h3 { font-size: 18px; color: var(--heading); margin-bottom: 6px; }

/* ══════════════════════════════════════════════════════════════════════════════
   PROBLEM DETAIL PAGE (problem.html)
══════════════════════════════════════════════════════════════════════════════ */

/* ── Detail sidebar ────────────────────────────────────────────────────────── */
.detail-sidebar .sidebar-inner { padding-top: 24px; }

.back-link {
  display: flex; align-items: center; gap: 8px;
  color: var(--sidebar-text);
  font-size: 13px;
  padding: 8px 10px;
  border-radius: 5px;
  margin-bottom: 20px;
  transition: background var(--transition), color var(--transition);
}

.back-link:hover {
  background: var(--sidebar-hover);
  color: var(--primary);
}

.problem-meta-card {
  background: rgba(255,255,255,.05);
  border: 1px solid rgba(255,255,255,.08);
  border-radius: var(--radius);
  padding: 16px;
  margin-bottom: 20px;
}

.meta-title {
  font-family: 'Raleway', sans-serif;
  font-size: 15px; font-weight: 700;
  color: #fff;
  line-height: 1.3;
  margin-bottom: 12px;
}

.meta-row {
  display: flex; align-items: center; justify-content: space-between;
  margin-bottom: 10px;
  font-size: 12px; color: var(--sidebar-text);
}

.meta-row:last-child { margin-bottom: 0; }

.meta-row .label {
  display: flex; align-items: center; gap: 6px;
  font-weight: 600; text-transform: uppercase;
  letter-spacing: .5px; font-size: 10px;
  color: rgba(168,178,193,.6);
}

.meta-row .value { font-weight: 600; color: #c8d3e0; }

.meta-tags {
  margin-top: 12px;
  padding-top: 12px;
  border-top: 1px solid rgba(255,255,255,.06);
  display: flex; flex-wrap: wrap; gap: 5px;
}

.meta-tag {
  font-size: 11px;
  background: rgba(20,157,221,.15);
  color: var(--primary);
  padding: 3px 9px; border-radius: 10px;
}

.leetcode-btn {
  display: flex; align-items: center; justify-content: center; gap: 8px;
  width: 100%; padding: 10px;
  background: var(--primary);
  color: #fff;
  border-radius: var(--radius);
  font-size: 13px; font-weight: 600;
  margin-top: 14px;
  transition: background var(--transition);
}

.leetcode-btn:hover { background: var(--primary-dark); color: #fff; }

/* ── Detail main ───────────────────────────────────────────────────────────── */
.detail-topbar {
  background: #fff;
  border-bottom: 1px solid var(--card-border);
  padding: 14px 28px;
  display: flex; align-items: center; gap: 12px;
  position: sticky; top: 0; z-index: 50;
}

.detail-topbar a {
  color: var(--text-muted); font-size: 13px;
  display: flex; align-items: center; gap: 4px;
}

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

.breadcrumb-sep { color: var(--card-border); }

.detail-topbar .current { color: var(--text); font-weight: 600; font-size: 13px; }

.detail-content-area { padding: 28px; }

/* ── Markdown rendered content ─────────────────────────────────────────────── */
.md-body {
  max-width: 860px;
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 32px 36px;
  box-shadow: var(--shadow);
}

.md-body h1, .md-body h2, .md-body h3, .md-body h4 {
  font-family: 'Raleway', sans-serif;
  color: var(--heading);
  line-height: 1.3;
  margin-top: 28px; margin-bottom: 12px;
}

.md-body h2 {
  font-size: 20px; font-weight: 700;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--primary);
  color: var(--primary);
}

.md-body h3 { font-size: 16px; font-weight: 700; }
.md-body h4 { font-size: 14px; font-weight: 700; color: var(--text-muted); }

.md-body p { margin-bottom: 12px; line-height: 1.7; }

.md-body ul, .md-body ol {
  margin: 0 0 12px 24px;
  line-height: 1.7;
}

.md-body blockquote {
  border-left: 3px solid var(--primary);
  background: #f0f9ff;
  padding: 10px 16px;
  margin: 12px 0;
  border-radius: 0 4px 4px 0;
  color: var(--text-muted);
  font-size: 13px;
}

.md-body blockquote strong { color: var(--text); }

.md-body strong { font-weight: 700; color: var(--heading); }

.md-body code:not([class]) {
  background: #f1f5f9;
  padding: 2px 6px; border-radius: 4px;
  font-family: 'Fira Code', 'Courier New', monospace;
  font-size: 13px; color: #e11d48;
}

.md-body pre {
  background: #1e293b;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: 16px 0;
  padding: 0;
}

.md-body pre code {
  display: block;
  padding: 18px 20px;
  font-family: 'Fira Code', 'Courier New', monospace;
  font-size: 13px;
  line-height: 1.7;
  color: #e2e8f0;
  background: transparent;
}

/* Prism.js overrides */
.md-body pre[class*="language-"] {
  background: #1e293b !important;
  border-radius: var(--radius);
  margin: 16px 0;
}

.md-body code[class*="language-"] {
  background: transparent !important;
  font-size: 13px !important;
  color: #e2e8f0 !important;
}

.md-body hr {
  border: none;
  border-top: 1px solid var(--card-border);
  margin: 20px 0;
}

.md-body table {
  width: 100%; border-collapse: collapse;
  margin: 16px 0; font-size: 14px;
}

.md-body th, .md-body td {
  padding: 8px 12px;
  border: 1px solid var(--card-border);
  text-align: left;
}

.md-body th {
  background: #f8fafc;
  font-weight: 700;
  color: var(--heading);
}

/* Loading state */
.loading-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--text-muted);
}

.loading-state i {
  font-size: 36px;
  display: block; margin-bottom: 12px;
  animation: spin .8s linear infinite;
}

@keyframes spin { to { transform: rotate(360deg); } }

.error-state {
  text-align: center;
  padding: 60px 20px;
  color: #dc2626;
}

/* ── Responsive ────────────────────────────────────────────────────────────── */
@media (max-width: 900px) {
  #sidebar {
    transform: translateX(-100%);
  }

  #sidebar.open {
    transform: translateX(0);
  }

  .sidebar-overlay.show {
    display: block;
  }

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

  #main {
    margin-left: 0;
  }

  .topbar, .detail-topbar {
    padding-left: 64px;
  }

  .grid-container {
    padding: 16px;
  }

  .detail-content-area {
    padding: 16px;
  }

  .md-body {
    padding: 20px 18px;
  }
}

@media (max-width: 600px) {
  .problems-grid {
    grid-template-columns: 1fr;
  }

  .topbar-title { font-size: 16px; }

  .md-body h2 { font-size: 17px; }
}