:root {
  --bg: #0e1116;
  --panel: #161b22;
  --fg: #c9d1d9;
  --muted: #8b949e;
  --accent: #58a6ff;
  --warn: #f85149;
  --ok: #3fb950;
  --kbd: #21262d;
  --border: #30363d;
}
* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; background: var(--bg); color: var(--fg);
  font: 16px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
header.topbar {
  position: sticky; top: 0; z-index: 10;
  background: var(--panel); border-bottom: 1px solid var(--border);
  padding: .8rem 1.5rem; display: flex; gap: 1rem; align-items: center;
}
header.topbar .title { font-weight: 700; }
header.topbar nav a { margin-right: 1rem; font-size: .9rem; }
main {
  max-width: 880px; margin: 2rem auto; padding: 0 1.5rem 4rem;
}
h1 { font-size: 2rem; border-bottom: 1px solid var(--border); padding-bottom: .4rem; }
h2 { font-size: 1.4rem; margin-top: 2.2rem; color: #e6edf3; }
h3 { font-size: 1.1rem; margin-top: 1.6rem; color: #e6edf3; }
.meta { color: var(--muted); font-size: .9rem; margin-top: -.5rem; }
pre {
  background: var(--panel); border: 1px solid var(--border); border-radius: 6px;
  padding: 1rem; overflow-x: auto; font-size: 13px; line-height: 1.45;
}
code { font-family: "SF Mono", Menlo, Consolas, monospace; }
:not(pre) > code {
  background: var(--kbd); padding: .12rem .35rem; border-radius: 4px; font-size: .92em;
}
blockquote {
  margin: 1rem 0; padding: .8rem 1rem;
  border-left: 4px solid var(--accent); background: var(--panel); border-radius: 4px;
}
blockquote.warn { border-left-color: var(--warn); }
blockquote.ok   { border-left-color: var(--ok); }
blockquote.q    { border-left-color: #d29922; }
blockquote.hint { border-left-color: #a371f7; }
blockquote .label {
  display: inline-block; font-size: .75rem; text-transform: uppercase;
  letter-spacing: .08em; color: var(--muted); margin-bottom: .3rem;
}
table { border-collapse: collapse; margin: 1rem 0; width: 100%; }
th, td { border: 1px solid var(--border); padding: .4rem .7rem; text-align: left; }
th { background: var(--panel); }
ul, ol { padding-left: 1.4rem; }
hr { border: none; border-top: 1px solid var(--border); margin: 2rem 0; }
.lesson-grid {
  display: grid; gap: 1rem; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}
.lesson-card {
  background: var(--panel); border: 1px solid var(--border); border-radius: 8px;
  padding: 1.2rem; display: flex; flex-direction: column;
}
.lesson-card h3 { margin: 0 0 .4rem 0; }
.lesson-card .num { color: var(--accent); font-weight: 700; font-size: .85rem; }
.lesson-card .status { font-size: .75rem; padding: .15rem .5rem; border-radius: 10px;
  display: inline-block; margin-top: .6rem; }
.status.done    { background: rgba(63,185,80,.15);  color: var(--ok); }
.status.wip     { background: rgba(210,153,34,.15); color: #d29922; }
.status.todo    { background: rgba(139,148,158,.15); color: var(--muted); }
.footer { color: var(--muted); font-size: .85rem; margin-top: 4rem; text-align: center; }
.diagram {
  background: #0a0d12; border: 1px solid var(--border);
  padding: 1rem; border-radius: 6px; overflow-x: auto;
  font-family: "SF Mono", Menlo, Consolas, monospace; font-size: 12.5px; line-height: 1.45;
  white-space: pre; color: #c9d1d9;
}
.lesson-nav {
  display: flex; justify-content: space-between; margin-top: 3rem;
  padding-top: 1rem; border-top: 1px solid var(--border);
}
.lesson-nav a { padding: .5rem .8rem; border: 1px solid var(--border); border-radius: 4px; }