:root {
  --bg: #0f172a;
  --bg-soft: #1e293b;
  --card: #1e293b;
  --border: #334155;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-2: #818cf8;
  --green: #34d399;
  --yellow: #fbbf24;
  --red: #f87171;
  --radius: 12px;
  --shadow: 0 10px 30px rgba(0, 0, 0, 0.35);
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: "Segoe UI", system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

a {
  color: var(--accent);
  text-decoration: none;
}

img {
  max-width: 100%;
}

.container {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 20px;
}

/* ===== Header ===== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(15, 23, 42, 0.9);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 20px;
  color: var(--text);
}

.brand .logo {
  display: grid;
  place-items: center;
  width: 36px;
  height: 36px;
  border-radius: 10px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #0f172a;
  font-weight: 800;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 22px;
  list-style: none;
}

.nav-links a {
  color: var(--muted);
  font-weight: 500;
  transition: color 0.2s;
}

.nav-links a:hover {
  color: var(--text);
}

.nav-links .nav-btn {
  padding: 8px 16px;
  border-radius: 8px;
  background: var(--accent);
  color: #0f172a;
  font-weight: 600;
  transition: transform 0.2s, opacity 0.2s;
}

.nav-links .nav-btn:hover {
  color: #0f172a;
  transform: translateY(-1px);
  opacity: 0.9;
}

/* ===== Hero ===== */
.hero {
  padding: 90px 0 70px;
  text-align: center;
  background: radial-gradient(600px 300px at 50% 0%, rgba(56, 189, 248, 0.15), transparent 70%);
}

.hero .badge {
  display: inline-block;
  padding: 6px 14px;
  border-radius: 999px;
  background: rgba(56, 189, 248, 0.12);
  border: 1px solid rgba(56, 189, 248, 0.35);
  color: var(--accent);
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 20px;
}

.hero h1 {
  font-size: clamp(34px, 6vw, 58px);
  line-height: 1.15;
  margin-bottom: 18px;
}

.hero h1 .grad {
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero p {
  max-width: 640px;
  margin: 0 auto 30px;
  color: var(--muted);
  font-size: 18px;
}

.hero-actions {
  display: flex;
  gap: 14px;
  justify-content: center;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 12px 24px;
  border-radius: 10px;
  font-weight: 600;
  border: 1px solid transparent;
  cursor: pointer;
  transition: transform 0.2s, opacity 0.2s;
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #0f172a;
}

.btn-primary:hover {
  transform: translateY(-2px);
  opacity: 0.95;
}

.btn-outline {
  border-color: var(--border);
  color: var(--text);
  background: transparent;
}

.btn-outline:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 40px;
  margin-top: 50px;
  flex-wrap: wrap;
}

.stat b {
  display: block;
  font-size: 28px;
  color: var(--text);
}

.stat span {
  color: var(--muted);
  font-size: 14px;
}

/* ===== Sections ===== */
.section {
  padding: 70px 0;
}

.section-head {
  text-align: center;
  max-width: 620px;
  margin: 0 auto 40px;
}

.section-head h2 {
  font-size: 30px;
  margin-bottom: 10px;
}

.section-head p {
  color: var(--muted);
}

/* ===== Course cards on home ===== */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 24px;
}

.course-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
  transition: transform 0.25s, border-color 0.25s, box-shadow 0.25s;
}

.course-card:hover {
  transform: translateY(-4px);
  border-color: var(--accent);
  box-shadow: var(--shadow);
}

.course-card .icon {
  display: grid;
  place-items: center;
  width: 52px;
  height: 52px;
  border-radius: 14px;
  font-size: 24px;
  margin-bottom: 18px;
}

.icon-html { background: rgba(249, 115, 22, 0.15); }
.icon-css { background: rgba(56, 189, 248, 0.15); }
.icon-js { background: rgba(250, 204, 21, 0.15); }

.course-card h3 {
  font-size: 20px;
  margin-bottom: 10px;
}

.course-card p {
  color: var(--muted);
  font-size: 15px;
  margin-bottom: 20px;
}

.course-card .meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 14px;
  color: var(--muted);
}

.shimmer {
  color: var(--muted);
  background: var(--muted);
}

.count {
  color: var(--muted);
  font-size: 14px;
}

/* progress bar */
.progress {
  height: 8px;
  border-radius: 99px;
  background: var(--border);
  overflow: hidden;
  margin-top: 16px;
}

.progress-inner {
  height: 100%;
  border-radius: 99px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  width: 0%;
  transition: width 0.4s;
}

/* ===== Lesson cards ===== */
.lesson-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
}

.lesson-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  display: flex;
  flex-direction: column;
  transition: transform 0.2s, border-color 0.2s;
}

.lesson-card:hover {
  transform: translateY(-3px);
  border-color: var(--accent);
}

.lesson-card .num {
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  margin-bottom: 12px;
}

.num-html { color: #fb923c; }
.num-css { color: var(--accent); }
.num-js { color: #facc15; }

.lesson-card h3 {
  font-size: 17px;
  margin-bottom: 8px;
  color: var(--text);
}

.lesson-card p {
  color: var(--muted);
  font-size: 14px;
  flex-grow: 1;
}

.lesson-card .go {
  margin-top: 16px;
  font-size: 14px;
  color: var(--accent);
}

.done {
  border-color: rgba(52, 211, 153, 0.4) !important;
}

.done .check {
  color: var(--green);
  font-size: 13px;
  margin-top: 8px;
  font-weight: 600;
}

/* ===== Features ===== */
.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 20px;
}

.feature {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
}

.feature .f-icon {
  font-size: 26px;
  margin-bottom: 12px;
}

.feature h4 {
  margin-bottom: 8px;
}

.feature p {
  color: var(--muted);
  font-size: 14px;
}

/* ===== Lesson page layout ===== */
.lesson-layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  gap: 32px;
  align-items: start;
  padding: 36px 0 60px;
}

.sidebar {
  position: sticky;
  top: 84px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
}

.sidebar h4 {
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--muted);
  margin-bottom: 12px;
}

.sidebar ul {
  list-style: none;
}

.sidebar li {
  border-radius: 8px;
  margin-bottom: 6px;
}

.sidebar a {
  display: block;
  padding: 8px 12px;
  font-size: 14px;
  color: var(--muted);
  border-radius: 8px;
  transition: background 0.2s, color 0.2s;
}

.sidebar a:hover {
  background: rgba(56, 189, 248, 0.1);
  color: var(--text);
}

.sidebar a.active {
  background: rgba(56, 189, 248, 0.15);
  color: var(--accent);
  font-weight: 600;
}

.lesson-body {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 36px;
  min-width: 0;
}

.lesson-body .num {
  font-size: 14px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--accent);
  font-weight: 700;
  display: block;
  margin-bottom: 8px;
}

.lesson-body h1 {
  font-size: 30px;
  margin-bottom: 8px;
}

.lesson-body .lead {
  color: var(--muted);
  margin-bottom: 28px;
}

.lesson-body h2 {
  font-size: 22px;
  margin: 34px 0 14px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

.lesson-body h3 {
  font-size: 17px;
  margin: 22px 0 10px;
}

.lesson-body p {
  margin-bottom: 14px;
}

.lesson-body ul,
.lesson-body ol {
  margin: 0 0 16px 22px;
}

.lesson-body li {
  margin-bottom: 6px;
}

.lesson-body strong {
  color: #fff;
}

/* code */
pre {
  background: #0b1220;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 16px 18px;
  overflow-x: auto;
  margin: 14px 0 20px;
}

code {
  font-family: "Cascadia Code", Consolas, "Courier New", monospace;
  font-size: 13.5px;
  color: #f8fafc;
}

:not(pre) > code {
  background: rgba(56, 189, 248, 0.12);
  color: #7dd3fc;
  padding: 2px 6px;
  border-radius: 5px;
  font-size: 13px;
}

.token.tag { color: #38bdf8; }
.token.attr { color: #fbbf24; }
.token.str  { color: #34d399; }
.token.cmt  { color: #64748b; font-style: italic; }
.token.num  { color: #f472b6; }
.token.key  { color: #c084fc; }
.token.fn   { color: #fbbf24; }

/* callout */
.callout {
  display: flex;
  gap: 12px;
  padding: 14px 18px;
  border-radius: 10px;
  margin: 18px 0;
  font-size: 15px;
}

.callout .e {
  font-size: 20px;
}

.callout.tip { background: rgba(52, 211, 153, 0.1); border-left: 4px solid var(--green); }
.callout.info { background: rgba(56, 189, 248, 0.1); border-left: 4px solid var(--accent); }
.callout.warn { background: rgba(251, 191, 36, 0.1); border-left: 4px solid var(--yellow); }

/* table */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 14px 0 22px;
  font-size: 14px;
}

th, td {
  text-align: left;
  padding: 10px 12px;
  border-bottom: 1px solid var(--border);
}

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

tr:hover td {
  background: rgba(56, 189, 248, 0.04);
}

/* practice / result boxes */
.result {
  background: #0b1220;
  border: 1px dashed var(--border);
  border-radius: 10px;
  padding: 20px;
  margin: 14px 0 20px;
}

.result .demo-row {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  align-items: center;
}

.demo-box {
  width: 64px;
  height: 64px;
  border-radius: 8px;
  background: var(--accent);
  color: #0f172a;
  display: grid;
  place-items: center;
  font-weight: 700;
}

.demo-box.green { background: var(--green); }
.demo-box.yellow { background: var(--yellow); }
.demo-box.red { background: var(--red); }
.demo-box.purple { background: var(--accent-2); }

.demo-strip {
  display: inline-flex;
  gap: 28px;
  border: 2px solid var(--green);
  padding: 18px 26px;
  border-radius: 12px;
}

.demo-pill {
  background: var(--green);
  color: #0f172a;
  padding: 6px 14px;
  border-radius: 999px;
  font-weight: 700;
}

/* progress + toggle */
#lessonProgress {
  display: inline-block;
  margin: 3px 0;
}

/* interactive demo */
.interactive {
  margin-top: 14px;
}

.interactive button,
.practice-control input {
  padding: 8px 14px;
  margin: 6px 6px 0 0;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-soft);
  color: var(--text);
  font-size: 14px;
  cursor: pointer;
}

.interactive button:hover {
  border-color: var(--accent);
  color: var(--accent);
}

#clickFeedback {
  margin-top: 12px;
  min-height: 24px;
  font-size: 15px;
}

/* lesson nav buttons */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 40px;
}

.lesson-nav .btn {
  border-color: var(--border);
  background: var(--bg-soft);
  color: var(--text);
}

.lesson-nav .btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

/* ===== Footer ===== */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 34px 0;
  text-align: center;
  color: var(--muted);
  font-size: 14px;
  margin-top: 40px;
}

.site-footer a {
  color: var(--muted);
  border-bottom: 1px dashed var(--border);
}

/* ===== Responsive ===== */
@media (max-width: 860px) {
  .lesson-layout {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
  }
}

@media (max-width: 640px) {
  .nav-links li:not(.nav-cta) {
    display: none;
  }

  .hero {
    padding: 60px 0 50px;
  }

  .lesson-body {
    padding: 24px 18px;
  }
}

/* ===== Sparkline/scrollbar ===== */
::-webkit-scrollbar {
  width: 10px;
  height: 10px;
}

::-webkit-scrollbar-track {
  background: var(--bg);
}

::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 99px;
}

::-webkit-scrollbar-thumb:hover {
  background: #475569;
}