/* StudyCorner — base theme. Hand-written (no build step) to stay
   toolchain-light. Light/dark via prefers-color-scheme. */
:root {
  --bg: #ffffff;
  --bg-soft: #f5f7fa;
  --bg-card: #ffffff;
  --ink: #1f2933;
  --ink-soft: #52606d;
  --muted: #7b8794;
  --line: #e1e7ee;
  --accent: #2563eb;
  --accent-soft: #eaf1fe;
  --radius: 12px;
  --maxw: 760px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono: "Cascadia Code", "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1620; --bg-soft: #151e2a; --bg-card: #18222f; --ink: #e4e9f0;
    --ink-soft: #b3c0cf; --muted: #8493a3; --line: #263240; --accent: #6ea8fe;
    --accent-soft: #1b2a40;
  }
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font-family: var(--font); line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Header / footer */
.site-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 24px; height: 56px; border-bottom: 1px solid var(--line);
  position: sticky; top: 0; background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px); z-index: 20;
}
.brand { font-weight: 700; font-size: 1.05rem; color: var(--ink); }
.brand span { color: var(--accent); }
.site-nav a { color: var(--ink-soft); font-size: .92rem; }
.site-footer {
  border-top: 1px solid var(--line); margin-top: 64px; padding: 24px;
  color: var(--muted); font-size: .82rem;
}
.site-footer p { max-width: var(--maxw); margin: 0 auto; }

.page { min-height: 60vh; }

/* Index / hero / cards */
.hero { max-width: var(--maxw); margin: 0 auto; padding: 56px 24px 8px; }
.hero h1 { font-size: 2.4rem; margin: 0 0 8px; letter-spacing: -.02em; }
.lede { font-size: 1.15rem; color: var(--ink-soft); }
.card-grid {
  max-width: 1080px; margin: 24px auto 0; padding: 0 24px 24px;
  display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 18px;
}
.card {
  display: block; background: var(--bg-card); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 20px; color: var(--ink);
  transition: border-color .15s, transform .15s, box-shadow .15s;
}
.card:hover { text-decoration: none; border-color: var(--accent); transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(37,99,235,.08); }
.card h2 { margin: 10px 0 6px; font-size: 1.25rem; }
.card p { margin: 0 0 14px; color: var(--ink-soft); font-size: .95rem; }
.card-type {
  display: inline-block; font-size: .7rem; text-transform: uppercase; letter-spacing: .08em;
  font-weight: 700; color: var(--accent); background: var(--accent-soft);
  padding: 3px 9px; border-radius: 999px;
}
.card-meta { color: var(--muted); font-size: .82rem; }

/* Two-column layout */
.layout {
  display: grid; grid-template-columns: 280px minmax(0, 1fr);
  max-width: 1180px; margin: 0 auto; gap: 40px; padding: 0 24px;
}
.sidebar { border-right: 1px solid var(--line); }
.sidebar-inner { position: sticky; top: 72px; max-height: calc(100vh - 88px);
  overflow-y: auto; padding: 28px 16px 28px 0; }
.sidebar-program { font-weight: 700; margin: 0 0 12px; font-size: .95rem; }
.toc-course-title { font-weight: 600; font-size: .82rem; text-transform: uppercase;
  letter-spacing: .05em; color: var(--muted); margin: 18px 0 4px; }
.toc-module-title { font-size: .85rem; color: var(--ink-soft); margin: 10px 0 2px; font-weight: 600; }
.toc ul { list-style: none; margin: 0 0 8px; padding: 0; }
.toc li a { display: block; padding: 4px 10px; border-radius: 7px; font-size: .9rem;
  color: var(--ink-soft); border-left: 2px solid transparent; }
.toc li a:hover { background: var(--bg-soft); text-decoration: none; }
.toc li a.current { color: var(--accent); background: var(--accent-soft);
  border-left-color: var(--accent); font-weight: 600; }

.content { padding: 28px 0 0; max-width: var(--maxw); }
.breadcrumb { font-size: .85rem; color: var(--muted); margin-bottom: 14px; }
.breadcrumb a { color: var(--muted); }
.breadcrumb span { margin: 0 6px; }

/* Lesson */
.lesson-position { color: var(--muted); font-size: .85rem; margin: 0 0 4px; text-transform: uppercase; letter-spacing: .05em; }
.lesson-head h1 { font-size: 2rem; margin: 0 0 12px; letter-spacing: -.02em; line-height: 1.2; }
.concepts { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 8px; }
.concept { font-size: .76rem; background: var(--bg-soft); border: 1px solid var(--line);
  color: var(--ink-soft); padding: 2px 9px; border-radius: 999px; cursor: help; }
.audience { background: var(--bg-soft); border-radius: var(--radius); padding: 12px 16px; color: var(--ink-soft); }
.program-stats { color: var(--muted); font-size: .9rem; }

/* Prose typography */
.prose { font-size: 1.04rem; }
.prose h2 { margin: 2em 0 .5em; font-size: 1.4rem; letter-spacing: -.01em; }
.prose h3 { margin: 1.6em 0 .4em; font-size: 1.15rem; }
.prose p { margin: 0 0 1.1em; }
.prose ul, .prose ol { padding-left: 1.4em; }
.prose li { margin: .3em 0; }
.prose blockquote {
  margin: 1.4em 0; padding: .6em 1.1em; border-left: 3px solid var(--accent);
  background: var(--bg-soft); border-radius: 0 8px 8px 0; color: var(--ink-soft);
}
.prose code { font-family: var(--mono); font-size: .88em; background: var(--bg-soft);
  padding: .12em .4em; border-radius: 5px; }
.prose pre { background: var(--bg-soft); border: 1px solid var(--line); border-radius: 10px;
  padding: 14px 16px; overflow-x: auto; }
.prose pre code { background: none; padding: 0; font-size: .85em; line-height: 1.55; }

/* Citations */
sup.cite { font-size: .72em; line-height: 0; }
sup.cite a { padding: 0 1px; }
sup.cite--missing { color: #d64545; }

/* Figures */
.figure { margin: 1.6em 0; text-align: center; }
.figure img { max-width: 100%; height: auto; border: 1px solid var(--line); border-radius: 10px; }
.figure figcaption { font-size: .86rem; color: var(--muted); margin-top: 8px; }

/* References */
.references { margin-top: 3em; border-top: 1px solid var(--line); padding-top: 1.2em; }
.references h2 { font-size: 1.25rem; }
.ref-list { font-size: .92rem; color: var(--ink-soft); }
.ref-list li { margin: .5em 0; }
.ref-list li:target { background: var(--accent-soft); border-radius: 6px; padding: 4px 8px; }
.ref-loc { display: block; color: var(--muted); font-size: .85em; margin-top: 2px; }
.ref-badge { font-size: .68rem; text-transform: uppercase; letter-spacing: .05em;
  padding: 1px 7px; border-radius: 999px; font-weight: 700; white-space: nowrap; }
.ref-badge--ok { background: #d7f5e3; color: #0c6b3f; }
.ref-badge--pending { background: #fdeccd; color: #8a5a00; }

/* Pager */
.pager { display: flex; justify-content: space-between; gap: 16px; margin-top: 3em;
  border-top: 1px solid var(--line); padding-top: 20px; }
.pager a { flex: 1; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 12px 16px; color: var(--ink); font-weight: 600; max-width: 48%; }
.pager a:hover { border-color: var(--accent); text-decoration: none; }
.pager a span { display: block; font-size: .72rem; text-transform: uppercase;
  letter-spacing: .06em; color: var(--muted); font-weight: 600; margin-bottom: 2px; }
.pager-next { text-align: right; margin-left: auto; }

/* Path (program landing) */
.path { list-style: none; padding: 0; counter-reset: c; }
.path-course { border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px 20px; margin-bottom: 16px; }
.path-course h3 { margin: 0 0 4px; }
.rationale { color: var(--ink-soft); font-size: .95rem; margin: 0 0 10px; font-style: italic; }
.path-module { font-weight: 600; color: var(--ink-soft); margin: 12px 0 2px; }

/* Planned (not-yet-authored) roadmap items */
.planned { color: var(--muted); }
.toc li .planned { display: block; padding: 4px 10px; font-size: .9rem; }
.path li .planned { color: var(--muted); }
.planned-tag { font-size: .62rem; text-transform: uppercase; letter-spacing: .06em;
  font-weight: 700; color: var(--muted); background: var(--bg-soft);
  border: 1px solid var(--line); padding: 1px 6px; border-radius: 999px;
  vertical-align: middle; }

/* Buttons */
.btn {
  display: inline-block; cursor: pointer; font: inherit; font-weight: 600;
  background: var(--accent); color: #fff; border: 1px solid var(--accent);
  border-radius: 999px; padding: 8px 16px; line-height: 1.2;
}
.btn:hover { text-decoration: none; filter: brightness(1.05); }
.btn--sm { padding: 5px 12px; font-size: .85rem; }
.btn--ghost { background: transparent; color: var(--ink-soft); border-color: var(--line); }
.btn--ghost:hover { border-color: var(--accent); color: var(--accent); }

/* Mark-complete toggle (lesson head) */
.mark-complete {
  cursor: pointer; font: inherit; font-size: .82rem; font-weight: 600;
  background: transparent; color: var(--ink-soft);
  border: 1px solid var(--line); border-radius: 999px; padding: 4px 14px; margin-top: 4px;
}
.mark-complete:hover { border-color: var(--accent); color: var(--accent); }
.mark-complete.is-complete {
  background: #d7f5e3; color: #0c6b3f; border-color: transparent;
}
@media (prefers-color-scheme: dark) {
  .mark-complete.is-complete { background: #14442e; color: #7fe3ad; }
}

/* Completion checkmarks on lesson links (sidebar + program path) */
.toc a.is-complete, .path a.is-complete { position: relative; }
.toc a.is-complete::after, .path li a.is-complete::after {
  content: "✓"; color: #2a9d6b; font-weight: 700; margin-left: 6px; font-size: .85em;
}
.path li a.is-complete { color: var(--muted); }

/* Progress bars (program landing + index cards) */
.progress { margin: 18px 0 6px; }
.progress-track {
  height: 8px; background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: 999px; overflow: hidden;
}
.progress-fill {
  display: block; height: 100%; width: 0; background: var(--accent);
  border-radius: 999px; transition: width .25s ease;
}
.progress.is-done .progress-fill { background: #2a9d6b; }
.progress-row { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-top: 8px; }
.progress-text { color: var(--muted); font-size: .85rem; }
.progress--mini { margin: 12px 0 0; }
.progress--mini .progress-text { display: block; margin-top: 6px; }

/* Progress tools (home page) */
.progress-tools {
  max-width: 1080px; margin: 8px auto 0; padding: 24px;
}
.progress-tools h2 { font-size: 1.2rem; margin: 0 0 6px; }
.progress-tools p { color: var(--ink-soft); font-size: .92rem; max-width: 60ch; }
.progress-tools-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 12px; }
.progress-tools-actions label { cursor: pointer; }

/* Self-check quiz */
.quiz {
  margin-top: 3em; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 20px 22px; background: var(--bg-soft);
}
.quiz-title { font-size: 1.25rem; margin: 0 0 6px; }
.quiz-list { list-style: none; counter-reset: q; padding: 0; margin: 0; }
.quiz-q { counter-increment: q; margin: 18px 0; }
.quiz-prompt { font-weight: 600; margin: 0 0 10px; }
.quiz-prompt::before { content: counter(q) ". "; color: var(--muted); }
.quiz-opts { list-style: none; padding: 0; margin: 0; display: grid; gap: 8px; }
.quiz-opt {
  cursor: pointer; padding: 9px 14px; border: 1px solid var(--line);
  border-radius: 9px; background: var(--bg-card); transition: border-color .12s, background .12s;
}
.quiz-opt:hover { border-color: var(--accent); }
.quiz-opt.is-selected { border-color: var(--accent); background: var(--accent-soft); }
.is-checked .quiz-opt { cursor: default; }
.quiz-opt.is-correct { border-color: #2a9d6b; background: #d7f5e3; color: #0c6b3f; }
.quiz-opt.is-wrong { border-color: #d64545; background: #fbe3e3; color: #8a1f1f; }
@media (prefers-color-scheme: dark) {
  .quiz-opt.is-correct { background: #14442e; color: #9be9c0; }
  .quiz-opt.is-wrong { background: #45201f; color: #f0a6a6; }
}
.quiz-explanation {
  margin: 8px 0 0; padding: 8px 12px; font-size: .92rem; color: var(--ink-soft);
  border-left: 3px solid var(--accent); background: var(--bg-card); border-radius: 0 8px 8px 0;
}
.quiz-actions { display: flex; align-items: center; gap: 14px; margin-top: 18px; }
.quiz-result { color: var(--ink-soft); font-weight: 600; font-size: .92rem; }

/* Responsive */
@media (max-width: 820px) {
  .layout { grid-template-columns: 1fr; gap: 0; }
  .sidebar { border-right: none; border-bottom: 1px solid var(--line); margin-bottom: 16px; }
  .sidebar-inner { position: static; max-height: none; padding: 16px 0; }
  .content { padding-top: 16px; }
  .pager a { max-width: none; }
}