:root {
  --bg: #edf2fa;
  --bg-alt: #e4ecf8;
  --panel: #ffffffcc;
  --panel-strong: #ffffff;
  --text: #111827;
  --muted: #4b5563;
  --accent: #2563eb;
  --accent-soft: #dbeafe;
  --border: #d9e3f0;
  --shadow: 0 16px 40px rgba(15, 23, 42, 0.08);
  --danger: #b42318;
}

[data-theme="dark"] {
  --bg: #0b1220;
  --bg-alt: #121b2f;
  --panel: rgba(20, 29, 47, 0.86);
  --panel-strong: #182338;
  --text: #e5eaf3;
  --muted: #b4c0d5;
  --accent: #6ca5ff;
  --accent-soft: rgba(108, 165, 255, 0.2);
  --border: #2b3a55;
  --shadow: 0 16px 40px rgba(0, 0, 0, 0.35);
  --danger: #ff8888;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
}

body {
  font-family: Inter, "Segoe UI", system-ui, -apple-system, sans-serif;
  background:
    radial-gradient(circle at top right, rgba(59, 130, 246, 0.15), transparent 45%),
    radial-gradient(circle at bottom left, rgba(14, 165, 233, 0.12), transparent 40%),
    linear-gradient(135deg, var(--bg), var(--bg-alt));
  color: var(--text);
}

a {
  color: var(--accent);
}

.app-shell {
  max-width: 1080px;
  margin: 0 auto;
  padding: 28px 16px 56px;
  display: grid;
  gap: 18px;
}

.site-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  backdrop-filter: blur(12px);
  box-shadow: var(--shadow);
  padding: 12px 16px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
}

.brand svg {
  width: 18px;
  height: 18px;
  fill: currentColor;
  opacity: 0.88;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

.nav-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 600;
  border: 1px solid transparent;
  border-radius: 999px;
  padding: 8px 12px;
}

.nav-link svg {
  width: 14px;
  height: 14px;
  fill: currentColor;
  opacity: 0.9;
}

.nav-link:hover,
.nav-link.active {
  color: var(--text);
  border-color: var(--border);
  background: var(--accent-soft);
}

.theme-toggle {
  min-width: 118px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(8px);
  padding: 20px;
}

.hero {
  background: linear-gradient(160deg, var(--panel-strong), var(--panel));
}

h1 {
  margin: 8px 0;
  font-size: clamp(1.65rem, 3vw, 2.15rem);
  line-height: 1.2;
  letter-spacing: -0.02em;
}

h2 {
  margin: 0 0 12px;
  font-size: 1.2rem;
  letter-spacing: -0.01em;
}

h3 {
  margin: 0 0 10px;
  font-size: 1rem;
}

p {
  line-height: 1.6;
}

.summary {
  margin: 0;
  color: var(--muted);
}

.hero-illustration {
  margin-top: 14px;
}

.hero-illustration svg {
  width: 100%;
  height: auto;
  display: block;
}

.badge {
  display: inline-flex;
  align-items: center;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  padding: 4px 10px;
  font-size: 0.78rem;
  font-weight: 700;
}

.header-row {
  margin-top: 10px;
  display: flex;
  gap: 12px;
  justify-content: space-between;
  align-items: flex-start;
  flex-wrap: wrap;
}

.action-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.button-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 10px;
}

button,
.button-link {
  border: 1px solid var(--border);
  background: var(--panel-strong);
  color: var(--text);
  border-radius: 10px;
  padding: 10px 13px;
  cursor: pointer;
  font-weight: 600;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
}

button:hover,
.button-link:hover {
  border-color: color-mix(in srgb, var(--accent) 35%, var(--border));
}

.danger-btn {
  color: var(--danger);
}

.progress-wrap {
  margin-top: 15px;
}

.progress-label {
  display: flex;
  justify-content: space-between;
  margin-bottom: 6px;
  color: var(--muted);
  font-size: 0.86rem;
}

.progress-track {
  width: 100%;
  height: 10px;
  background: color-mix(in srgb, var(--accent-soft) 70%, transparent);
  border-radius: 999px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), #38bdf8);
}

.search-wrap {
  display: grid;
  gap: 6px;
  margin-top: 14px;
  color: var(--muted);
  font-size: 0.86rem;
}

input[type="search"],
input[type="text"],
input[type="number"],
textarea,
select {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 12px;
  font: inherit;
  color: var(--text);
  background: var(--panel-strong);
}

.task-card {
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px;
  margin-bottom: 10px;
  background: var(--panel-strong);
}

.task-complete {
  border-color: color-mix(in srgb, var(--accent) 40%, var(--border));
  background: color-mix(in srgb, var(--accent-soft) 40%, var(--panel-strong));
}

.checkbox-wrap {
  font-weight: 600;
  display: flex;
  align-items: flex-start;
  gap: 8px;
}

.task-details {
  margin: 8px 0 10px 24px;
  color: var(--muted);
  font-size: 0.95rem;
}

.note-label {
  margin-left: 24px;
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 0.85rem;
}

textarea {
  resize: vertical;
  min-height: 80px;
}

.empty-state {
  color: var(--muted);
  margin: 0;
}

.tips-panel ul {
  margin: 0;
  padding-left: 18px;
  display: grid;
  gap: 7px;
  color: var(--muted);
}

.small-muted {
  color: var(--muted);
  font-size: 0.86rem;
}

.quick-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 8px;
}

.quick-list-item a {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 12px;
  background: var(--panel-strong);
  text-decoration: none;
  color: var(--text);
}

.quick-list-item a:hover {
  border-color: color-mix(in srgb, var(--accent) 35%, var(--border));
}

.chip-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.chip {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 5px 10px;
  font-size: 0.75rem;
  color: var(--muted);
}

.category-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 12px;
}

.category-card {
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px;
  background: var(--panel-strong);
}

.category-card ul {
  margin: 0;
  padding-left: 16px;
  display: grid;
  gap: 6px;
}

.fundamentals-grid {
  display: grid;
  gap: 12px;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}

.osi-diagram {
  display: grid;
  gap: 8px;
  margin-bottom: 10px;
}

.osi-diagram-layer {
  justify-content: flex-start;
  border-radius: 12px;
  background: linear-gradient(90deg, color-mix(in srgb, var(--accent-soft) 75%, transparent), var(--panel-strong));
}

.command-grid {
  display: grid;
  gap: 10px;
}

.command-card {
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 12px;
  background: color-mix(in srgb, var(--panel-strong) 85%, var(--accent-soft));
}

.command-card code {
  display: block;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.85rem;
  color: var(--text);
  margin-bottom: 6px;
  white-space: pre-wrap;
  word-break: break-word;
}

.command-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.86rem;
}

.osi-layers {
  display: grid;
  gap: 8px;
}

.osi-btn {
  justify-content: flex-start;
}

.subnet-result {
  margin-top: 10px;
  border: 1px dashed var(--border);
  border-radius: 12px;
  padding: 10px;
  color: var(--muted);
  font-size: 0.92rem;
}

.table-wrap {
  overflow-x: auto;
}

.method-grid {
  display: grid;
  gap: 12px;
}

.method-card {
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px;
  background: var(--panel-strong);
}

.method-card ul,
.method-checklist {
  margin: 8px 0 0;
  padding-left: 18px;
  display: grid;
  gap: 6px;
  color: var(--muted);
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
}

th,
td {
  border-bottom: 1px solid var(--border);
  text-align: left;
  padding: 9px 8px;
}

th {
  color: var(--muted);
  font-weight: 600;
}

@media (max-width: 720px) {
  .site-nav {
    align-items: flex-start;
    flex-direction: column;
  }

  .nav-links {
    width: 100%;
  }

  .theme-toggle {
    width: 100%;
  }
}

@media print {
  .site-nav,
  .page-header button,
  .page-header input {
    display: none !important;
  }

  .page-header {
    position: static;
  }

  body {
    background: #fff;
    color: #111;
  }

  .panel,
  .task-card {
    box-shadow: none;
    border-color: #ccc;
    background: #fff;
  }
}