:root {
  --bg: #0b0f14;
  --bg-2: #111720;
  --panel: #151c27;
  --panel-2: #1b2431;
  --border: #263142;
  --text: #e6edf3;
  --muted: #8b98a9;
  --accent: #22c55e;
  --accent-ink: #052e14;
  --blue: #60a5fa;
  --yellow: #facc15;
  --red: #f87171;
  --purple: #c084fc;
  --code-bg: #0e141c;
  --radius: 10px;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", "JetBrains Mono", Menlo, Consolas, monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, Ubuntu, sans-serif;
  color-scheme: dark;
}

:root[data-theme="light"] {
  --bg: #f6f8fa;
  --bg-2: #eef1f5;
  --panel: #ffffff;
  --panel-2: #f3f5f8;
  --border: #d5dbe3;
  --text: #1a2230;
  --muted: #5b6878;
  --accent: #16a34a;
  --accent-ink: #ffffff;
  --blue: #2563eb;
  --yellow: #a16207;
  --red: #dc2626;
  --purple: #7c3aed;
  --code-bg: #f3f5f8;
  color-scheme: light;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--bg);
  color: var(--text);
  font: 15px/1.6 var(--sans);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
a { color: var(--blue); }
code, pre { font-family: var(--mono); }
main { flex: 1; outline: none; }

/* ---------- Top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; gap: 20px;
  padding: 10px 20px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}
.brand { font-weight: 700; font-size: 18px; color: var(--text); text-decoration: none; display: flex; align-items: center; gap: 8px; }
.brand-mark {
  font-family: var(--mono); font-size: 13px; background: var(--accent); color: #0b0f14;
  border-radius: 6px; padding: 2px 6px;
}
.topnav { display: flex; gap: 16px; }
.topnav a { color: var(--muted); text-decoration: none; font-weight: 500; }
.topnav a:hover, .topnav a.active { color: var(--text); }
.topbar-right { margin-left: auto; display: flex; align-items: center; gap: 12px; }
.xp { font-family: var(--mono); font-size: 13px; color: var(--yellow); }
.icon-btn {
  background: var(--panel); color: var(--text); border: 1px solid var(--border);
  border-radius: 8px; width: 34px; height: 34px; cursor: pointer; font-size: 16px;
}

.footer { color: var(--muted); font-size: 12px; text-align: center; padding: 16px; border-top: 1px solid var(--border); }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 6px;
  font: 600 14px var(--sans);
  padding: 8px 14px; border-radius: 8px; cursor: pointer;
  border: 1px solid var(--border); background: var(--panel-2); color: var(--text);
  text-decoration: none;
}
.btn:hover { border-color: var(--muted); }
.btn:disabled { opacity: .55; cursor: progress; }
.btn-primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn-primary:hover { filter: brightness(1.1); border-color: var(--accent); }
.btn-ghost { background: transparent; }
.btn-sm { padding: 5px 10px; font-size: 13px; }

/* ---------- Home ---------- */
.container { max-width: 1100px; margin: 0 auto; padding: 32px 20px 48px; }
.hero h1 { font-size: clamp(28px, 4vw, 40px); line-height: 1.15; margin: 8px 0 12px; }
.hero p { color: var(--muted); max-width: 640px; font-size: 16px; margin: 0 0 8px; }
.hero .eyebrow { font-family: var(--mono); color: var(--accent); font-size: 13px; }
.stats { display: flex; gap: 12px; flex-wrap: wrap; margin: 20px 0 28px; }
.stat { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); padding: 10px 16px; min-width: 130px; }
.stat b { display: block; font-size: 22px; font-family: var(--mono); }
.stat span { color: var(--muted); font-size: 12px; }

.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 16px; }
.card {
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 18px; text-decoration: none; color: var(--text);
  display: flex; flex-direction: column; gap: 10px;
  transition: transform .12s ease, border-color .12s ease;
}
.card:hover { transform: translateY(-2px); border-color: var(--track, var(--accent)); }
.card-icon {
  width: 42px; height: 42px; border-radius: 10px; display: grid; place-items: center;
  font: 700 15px var(--mono); color: #0b0f14; background: var(--track, var(--accent));
}
.card h3 { margin: 0; font-size: 18px; }
.card p { margin: 0; color: var(--muted); font-size: 14px; flex: 1; }
.progress { height: 6px; background: var(--bg-2); border-radius: 99px; overflow: hidden; }
.progress > i { display: block; height: 100%; background: var(--track, var(--accent)); border-radius: 99px; }
.card small { color: var(--muted); font-size: 12px; font-family: var(--mono); }

.section-title { margin: 36px 0 12px; font-size: 18px; }
.playground-links { display: flex; gap: 10px; flex-wrap: wrap; }

/* ---------- Track page ---------- */
.crumbs { font-size: 13px; color: var(--muted); margin-bottom: 8px; }
.crumbs a { color: var(--muted); }
.track-head { display: flex; gap: 16px; align-items: center; margin-bottom: 8px; }
.track-head h1 { margin: 0; }
.notice {
  border: 1px solid color-mix(in srgb, var(--yellow) 45%, var(--border));
  background: color-mix(in srgb, var(--yellow) 8%, var(--panel));
  border-radius: var(--radius); padding: 12px 16px; margin: 16px 0; font-size: 14px;
}
.notice strong { color: var(--yellow); }
.lesson-list { list-style: none; padding: 0; margin: 20px 0 0; display: grid; gap: 8px; }
.lesson-list a {
  display: flex; align-items: center; gap: 14px; padding: 12px 16px;
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  color: var(--text); text-decoration: none;
}
.lesson-list a:hover { border-color: var(--track, var(--accent)); }
.lesson-num {
  width: 30px; height: 30px; border-radius: 50%; display: grid; place-items: center; flex: none;
  font: 600 13px var(--mono); background: var(--bg-2); color: var(--muted); border: 1px solid var(--border);
}
.done .lesson-num { background: var(--accent); color: #0b0f14; border-color: var(--accent); }
.lesson-list .meta { color: var(--muted); font-size: 13px; margin-left: auto; font-family: var(--mono); }

/* ---------- Lesson workspace ---------- */
.workspace {
  display: grid; grid-template-columns: minmax(320px, 42%) 1fr;
  height: calc(100vh - 56px);
  min-height: 560px;
}
.lesson-pane { overflow-y: auto; border-right: 1px solid var(--border); padding: 20px 24px 32px; }
.lesson-pane h1 { font-size: 24px; margin: 4px 0 12px; line-height: 1.25; }
.lesson-pane h2 { font-size: 17px; margin: 22px 0 8px; }
.lesson-pane p, .lesson-pane li { color: color-mix(in srgb, var(--text) 88%, var(--muted)); }
.lesson-pane code {
  background: var(--code-bg); border: 1px solid var(--border);
  padding: 1px 5px; border-radius: 5px; font-size: 13px;
}
.lesson-pane pre {
  background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 12px 14px; overflow-x: auto; font-size: 13px; line-height: 1.5;
}
.lesson-pane pre code { background: none; border: 0; padding: 0; }
.task {
  border-left: 3px solid var(--track, var(--accent));
  background: var(--panel); border-radius: 0 8px 8px 0; padding: 10px 16px; margin: 20px 0;
}
.task h2 { margin-top: 4px; }
.tip { color: var(--muted); font-size: 14px; }
.warn {
  border: 1px solid color-mix(in srgb, var(--red) 45%, var(--border));
  background: color-mix(in srgb, var(--red) 8%, var(--panel));
  border-radius: 8px; padding: 10px 14px; font-size: 14px;
}
.hint-box {
  margin-top: 12px; border: 1px dashed var(--border); border-radius: 8px; padding: 10px 14px;
  color: var(--text); background: var(--panel); font-size: 14px;
}
.lesson-nav { display: flex; justify-content: space-between; gap: 10px; margin-top: 28px; }

.editor-pane { display: flex; flex-direction: column; min-width: 0; min-height: 0; }
.toolbar {
  display: flex; align-items: center; gap: 8px; padding: 8px 12px;
  border-bottom: 1px solid var(--border); background: var(--bg-2); flex-wrap: wrap;
}
.toolbar .spacer { flex: 1; }
.lang-pill { font: 600 12px var(--mono); color: var(--muted); padding: 3px 8px; border: 1px solid var(--border); border-radius: 99px; }
.editor-wrap { flex: 1 1 55%; min-height: 160px; position: relative; overflow: hidden; }
.editor-wrap .CodeMirror { position: absolute; inset: 0; height: 100%; font: 14px/1.55 var(--mono); }
.editor-wrap textarea.fallback {
  position: absolute; inset: 0; width: 100%; height: 100%; resize: none; border: 0; padding: 12px;
  background: var(--code-bg); color: var(--text); font: 14px/1.55 var(--mono); tab-size: 4;
}
:root[data-theme="light"] .cm-s-dracula.CodeMirror,
:root[data-theme="light"] .cm-s-dracula .CodeMirror-gutters { background: #fbfcfd !important; color: #1a2230 !important; }
:root[data-theme="light"] .cm-s-dracula .CodeMirror-cursor { border-left-color: #1a2230; }
:root[data-theme="light"] .cm-s-dracula span.cm-string { color: #a15c00; }
:root[data-theme="light"] .cm-s-dracula span.cm-keyword { color: #c2185b; }
:root[data-theme="light"] .cm-s-dracula span.cm-number { color: #6d28d9; }
:root[data-theme="light"] .cm-s-dracula span.cm-comment { color: #6b7280; }
:root[data-theme="light"] .cm-s-dracula span.cm-def,
:root[data-theme="light"] .cm-s-dracula span.cm-variable-2 { color: #15803d; }
:root[data-theme="light"] .cm-s-dracula span.cm-tag { color: #c2185b; }
:root[data-theme="light"] .cm-s-dracula span.cm-attribute { color: #15803d; }
:root[data-theme="light"] .cm-s-dracula span.cm-variable,
:root[data-theme="light"] .cm-s-dracula span.cm-property { color: #1a2230; }
:root[data-theme="light"] .cm-s-dracula span.cm-builtin { color: #0369a1; }
:root[data-theme="light"] .cm-s-dracula .CodeMirror-selected { background: #dbeafe !important; }

.output-pane { flex: 1 1 45%; min-height: 140px; display: flex; flex-direction: column; border-top: 1px solid var(--border); }
.output-tabs { display: flex; gap: 2px; padding: 6px 10px 0; background: var(--bg-2); border-bottom: 1px solid var(--border); }
.output-tabs button {
  background: none; border: 0; color: var(--muted); font: 600 13px var(--sans); padding: 6px 12px; cursor: pointer;
  border-bottom: 2px solid transparent;
}
.output-tabs button.active { color: var(--text); border-bottom-color: var(--track, var(--accent)); }
.output {
  flex: 1; overflow: auto; margin: 0; padding: 12px 14px; background: var(--code-bg);
  font: 13px/1.55 var(--mono); white-space: pre-wrap; word-break: break-word;
}
.output .err { color: var(--red); }
.output .ok { color: var(--accent); font-weight: 700; }
.output .fail { color: var(--yellow); font-weight: 700; }
.output .sys { color: var(--muted); font-style: italic; }
.preview { flex: 1; border: 0; width: 100%; background: #fff; }
.stdin-box {
  width: 100%; border: 0; border-top: 1px solid var(--border); background: var(--bg-2); color: var(--text);
  font: 13px var(--mono); padding: 8px 12px; resize: vertical; min-height: 38px;
}
.hidden { display: none !important; }

.toast {
  position: fixed; bottom: 24px; left: 50%; transform: translateX(-50%) translateY(20px);
  background: var(--accent); color: #0b0f14; font-weight: 700; padding: 10px 18px; border-radius: 99px;
  opacity: 0; transition: all .25s ease; pointer-events: none; z-index: 50;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }

/* ---------- Responsive ---------- */
@media (max-width: 860px) {
  .workspace { grid-template-columns: 1fr; height: auto; }
  .lesson-pane { border-right: 0; border-bottom: 1px solid var(--border); padding: 16px; }
  .editor-pane { height: 85vh; }
  .topbar { padding: 10px 16px; gap: 12px; }
  .container { padding: 24px 16px 40px; }
}
@media (max-width: 480px) {
  .topnav a:last-child { display: none; }
  .xp { display: none; }
}