/* ============================================================
   Backend Engineering Course — Shared Stylesheet
   Light theme · system fonts · 70ch content · HiDPI-ready
   ============================================================ */

/* --- Custom properties ------------------------------------ */
:root {
  --bg:          #f5f4f0;
  --surface:     #ffffff;
  --surface-2:   #faf9f7;
  --border:      #e4dfd7;
  --border-soft: #ede9e3;
  --text:        #18212f;
  --text-2:      #4a5568;
  --muted:       #8492a6;
  --accent:      #2563eb;
  --accent-2:    #1d4ed8;
  --accent-bg:   #eff6ff;
  --accent-glow: rgba(37,99,235,0.12);
  --success:     #16a34a;
  --success-bg:  #f0fdf4;
  --warning:     #b45309;
  --warning-bg:  #fffbeb;
  --danger:      #dc2626;
  --ee-bg:       #fdf4ff;
  --ee-border:   #c084fc;
  --ee-text:     #6b21a8;

  --radius:    6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow:    0 1px 4px rgba(0,0,0,0.07), 0 2px 8px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.08), 0 1px 4px rgba(0,0,0,0.04);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.10), 0 2px 8px rgba(0,0,0,0.05);

  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono: "SF Mono", "Fira Code", "Cascadia Code", Menlo, Consolas, monospace;

  --content-w: 70ch;
  --page-w:    920px;
  --lh:        1.75;
}

/* --- Reset ------------------------------------------------ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 16px; scroll-behavior: smooth; -webkit-font-smoothing: antialiased; }
body { font-family: var(--font); background: var(--bg); color: var(--text); line-height: var(--lh); min-height: 100vh; }
img { max-width: 100%; display: block; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
button { font-family: var(--font); }

/* --- Top bar ---------------------------------------------- */
.topbar {
  position: sticky; top: 0; z-index: 200;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  max-width: var(--page-w);
  margin: 0 auto;
  padding: 0.7rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.course-home-link {
  font-size: 0.9rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text);
}
.course-home-link:hover { color: var(--accent); text-decoration: none; }
.breadcrumb {
  font-size: 0.8rem;
  color: var(--muted);
  display: flex;
  align-items: center;
  gap: 0.3rem;
  flex-wrap: wrap;
}
.breadcrumb .sep { opacity: 0.4; }
.breadcrumb .current { color: var(--text); font-weight: 500; }

/* Thin progress bar under topbar */
.progress-bar-thin {
  height: 2px;
  background: var(--border);
  position: relative;
  overflow: hidden;
}
.progress-bar-thin::after {
  content: "";
  position: absolute;
  inset: 0;
  right: auto;
  background: linear-gradient(90deg, var(--accent), #60a5fa);
  width: var(--progress, 0%);
  transition: width 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ============================================================
   HOME PAGE
   ============================================================ */

.home-wrap {
  max-width: var(--page-w);
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
}

/* Progress hero card */
.progress-hero {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.75rem 2rem;
  margin-bottom: 2.5rem;
  box-shadow: var(--shadow-md);
  position: relative;
  overflow: hidden;
}
.progress-hero::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), #60a5fa, #a78bfa);
}

.hero-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1.5rem;
  flex-wrap: wrap;
  margin-bottom: 1.25rem;
}

.hero-pct {
  font-size: 3rem;
  font-weight: 800;
  letter-spacing: -0.05em;
  line-height: 1;
  background: linear-gradient(135deg, var(--accent), #60a5fa);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-pct-label {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
  margin-top: 0.2rem;
}

.hero-stats {
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
}
.hero-stat {
  text-align: center;
}
.hero-stat-value {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  color: var(--text);
  line-height: 1;
}
.hero-stat-label {
  font-size: 0.75rem;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 0.2rem;
}

/* Progress bar (fat) */
.hero-bar-wrap {
  height: 8px;
  background: var(--bg);
  border-radius: 99px;
  overflow: hidden;
  margin-bottom: 1.5rem;
  border: 1px solid var(--border-soft);
}
.hero-bar-fill {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--accent), #60a5fa);
  border-radius: 99px;
  transition: width 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Action buttons */
.hero-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
}
.btn-resume {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--accent);
  color: #fff;
  font-weight: 600;
  font-size: 0.88rem;
  padding: 0.6rem 1.25rem;
  border-radius: var(--radius-md);
  transition: background 0.15s, transform 0.1s, box-shadow 0.15s;
  box-shadow: 0 2px 8px var(--accent-glow);
  line-height: 1.4;
}
.btn-resume:hover { background: var(--accent-2); text-decoration: none; transform: translateY(-1px); box-shadow: 0 4px 12px var(--accent-glow); }
.btn-resume:active { transform: translateY(0); }
.btn-resume .btn-icon { font-style: normal; }

.btn-reset {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--surface);
  color: var(--text-2);
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.6rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all 0.15s;
  line-height: 1.4;
}
.btn-reset:hover { border-color: var(--danger); color: var(--danger); }

/* ---- Week sections --------------------------------------- */
.schedule-week {
  margin-bottom: 2rem;
}

.week-label {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.9rem;
}
.week-num {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  background: var(--accent-bg);
  color: var(--accent);
  padding: 0.2rem 0.6rem;
  border-radius: 99px;
}
.week-num.locked { background: var(--bg); color: var(--muted); }
.week-title {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text);
}
.week-coming {
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
  background: var(--bg);
  border: 1px solid var(--border);
  padding: 0.15rem 0.55rem;
  border-radius: 99px;
}

/* Day cards grid */
.days-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 0.75rem;
}

.day-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1rem 1.125rem;
  box-shadow: var(--shadow-sm);
  transition: box-shadow 0.2s, border-color 0.2s, transform 0.15s;
  position: relative;
}
.day-card:hover:not(.day-card--locked) {
  box-shadow: var(--shadow);
  border-color: #c7d8ff;
  transform: translateY(-1px);
}
.day-card--complete { border-left: 3px solid var(--success); }
.day-card--locked {
  opacity: 0.55;
  cursor: default;
}

.day-card-head {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 0.65rem;
}
.day-pill {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 0.18rem 0.5rem;
  border-radius: 99px;
  white-space: nowrap;
}
.day-pill--active   { background: var(--accent-bg);  color: var(--accent); }
.day-pill--done     { background: var(--success-bg); color: var(--success); }
.day-pill--locked   { background: var(--bg);         color: var(--muted); }

.day-card-title { font-size: 0.88rem; font-weight: 600; color: var(--text); }
.day-prog {
  margin-left: auto;
  font-size: 0.75rem;
  color: var(--muted);
  font-weight: 500;
}

/* Lesson list */
.lesson-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}
.lesson-row {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.lesson-dot {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.6rem;
  transition: all 0.2s;
}
.lesson-dot--done {
  background: var(--success);
  border-color: var(--success);
  color: #fff;
}
.lesson-row a {
  font-size: 0.83rem;
  color: var(--text-2);
  transition: color 0.15s;
  line-height: 1.35;
}
.lesson-row a:hover { color: var(--accent); text-decoration: none; }
.lesson-row--done a { color: var(--muted); }
.lesson-row--locked a {
  color: var(--muted);
  pointer-events: none;
  cursor: default;
}
.lesson-row--locked .lesson-dot { border-style: dashed; }

/* ============================================================
   LESSON PAGE
   ============================================================ */
.lesson-wrap {
  max-width: calc(var(--content-w) + 3rem);
  margin: 0 auto;
  padding: 2.5rem 1.5rem 6rem;
}

.lesson-wrap h1 {
  font-size: 1.8rem;
  font-weight: 800;
  letter-spacing: -0.035em;
  line-height: 1.22;
  margin-bottom: 1.25rem;
}
.lesson-wrap h2 {
  font-size: 1.15rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin: 2rem 0 0.65rem;
}
.lesson-wrap h3 {
  font-size: 1rem;
  font-weight: 600;
  margin: 1.4rem 0 0.45rem;
}
.lesson-wrap p  { margin-bottom: 1rem; }
.lesson-wrap ul, .lesson-wrap ol { margin: 0.4rem 0 1rem 1.4rem; }
.lesson-wrap li { margin-bottom: 0.3rem; }
.lesson-wrap strong { font-weight: 600; }
.lesson-wrap table {
  border-collapse: collapse;
  width: 100%;
  margin: 1rem 0;
  font-size: 0.87rem;
}
.lesson-wrap th, .lesson-wrap td {
  border: 1px solid var(--border);
  padding: 0.5rem 0.75rem;
  text-align: left;
}
.lesson-wrap th { background: var(--bg); font-weight: 600; }
.lesson-wrap tr:hover td { background: var(--surface-2); }

/* Hook */
.hook {
  background: linear-gradient(135deg, var(--accent-bg) 0%, #f0f4ff 100%);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  padding: 1.25rem 1.5rem;
  margin-bottom: 2rem;
}
.hook .hook-label {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  margin-bottom: 0.4rem;
}
.hook h1 { font-size: 1.7rem; margin-bottom: 0.65rem; }
.hook p  { margin-bottom: 0; font-size: 1rem; color: var(--text-2); }

/* Callout boxes */
.callout {
  border-radius: var(--radius-md);
  padding: 0.9rem 1.125rem;
  margin: 1.25rem 0;
  font-size: 0.92rem;
}
.callout-label {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 0.35rem;
}
.callout p:last-child { margin-bottom: 0; }

.callout-ee    { background: var(--ee-bg);     border: 1px solid var(--ee-border); }
.callout-ee    .callout-label { color: var(--ee-text); }
.callout-watch { background: var(--warning-bg); border: 1px solid #fcd34d; }
.callout-watch .callout-label { color: var(--warning); }
.callout-tip   { background: var(--success-bg); border: 1px solid #86efac; }
.callout-tip   .callout-label { color: var(--success); }

/* Code */
pre, code { font-family: var(--mono); }
code {
  background: #eef0f5;
  padding: 0.1em 0.35em;
  border-radius: 4px;
  font-size: 0.875em;
}
pre {
  background: #1a2035;
  color: #e2e8f0;
  padding: 1.25rem 1.5rem;
  border-radius: var(--radius-lg);
  overflow-x: auto;
  margin: 0.75rem 0;
  line-height: 1.6;
  font-size: 0.85rem;
  box-shadow: var(--shadow);
}
pre code { background: none; padding: 0; font-size: inherit; color: inherit; }

/* Collapsible: Going Deeper */
.going-deeper {
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  margin: 1.75rem 0;
  overflow: hidden;
}
.going-deeper > summary {
  padding: 0.85rem 1.25rem;
  cursor: pointer;
  font-weight: 600;
  font-size: 0.92rem;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--surface);
  user-select: none;
  transition: background 0.15s;
}
.going-deeper > summary::-webkit-details-marker { display: none; }
.going-deeper > summary::before {
  content: "▶";
  font-size: 0.6rem;
  color: var(--muted);
  transition: transform 0.2s;
  flex-shrink: 0;
}
.going-deeper[open] > summary::before { transform: rotate(90deg); }
.going-deeper > summary:hover { background: var(--bg); }
.going-deeper .deeper-content {
  padding: 1.125rem 1.5rem;
  border-top: 1px solid var(--border);
  background: var(--surface);
}
.going-deeper .deeper-content p:last-child { margin-bottom: 0; }

/* Exercise section */
.exercise-section {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  margin: 1.75rem 0;
  overflow: hidden;
  box-shadow: var(--shadow);
}
.exercise-header {
  padding: 0.85rem 1.25rem;
  background: #1a2035;
  color: #e2e8f0;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}
.exercise-label {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: #94a3b8;
}
.exercise-header h3 {
  margin: 0;
  font-size: 0.92rem;
  font-weight: 600;
  color: #e2e8f0;
}
.exercise-body { padding: 1.125rem 1.5rem; }
.exercise-body p:last-of-type { margin-bottom: 0.75rem; }
.exercise-body pre { margin-top: 0; }

.solution-toggle {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.82rem;
  padding: 0.42rem 0.875rem;
  border-radius: var(--radius);
  cursor: pointer;
  margin-top: 0.75rem;
  transition: all 0.15s;
}
.solution-toggle:hover { border-color: var(--accent); color: var(--accent); }
.solution-block { display: none; margin-top: 0.75rem; padding-top: 0.75rem; border-top: 1px solid var(--border); }
.solution-block.visible { display: block; }

/* Recap */
.recap-section {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.125rem 1.5rem;
  margin: 1.75rem 0;
}
.recap-section h2 { margin-top: 0; }
.recap-section ul { margin-left: 0; list-style: none; }
.recap-section li { padding: 0.28rem 0 0.28rem 1.4rem; position: relative; }
.recap-section li::before {
  content: "✓";
  position: absolute; left: 0;
  color: var(--success); font-weight: 700;
}

/* Wonder */
.wonder-section { margin: 1.75rem 0; }
.wonder-section h2 { margin-bottom: 0.65rem; }
.wonder-section ol { margin-left: 1.4rem; }
.wonder-section li { margin-bottom: 0.5rem; font-style: italic; color: var(--text-2); }
.wonder-section li::marker { color: var(--accent); font-style: normal; }

/* ---- Lesson footer (fixed) ------------------------------- */
.lesson-footer {
  position: fixed;
  bottom: 0; left: 0; right: 0;
  background: rgba(255,255,255,0.94);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-top: 1px solid var(--border);
  padding: 0.7rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  z-index: 100;
  box-shadow: 0 -2px 16px rgba(0,0,0,0.06);
}
.btn-complete {
  background: var(--accent);
  color: #fff;
  border: none;
  font-size: 0.86rem;
  font-weight: 600;
  padding: 0.52rem 1.125rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background 0.15s, transform 0.1s;
}
.btn-complete:hover { background: var(--accent-2); }
.btn-complete:active { transform: scale(0.98); }
.btn-complete.done { background: var(--success); cursor: default; }

.lesson-nav { display: flex; align-items: center; gap: 0.6rem; }
.nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.84rem;
  font-weight: 500;
  color: var(--text-2);
  padding: 0.48rem 0.875rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  text-decoration: none;
  transition: all 0.15s;
  white-space: nowrap;
}
.nav-btn:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; }
.nav-btn.hidden { visibility: hidden; }

/* ---- Diagram container ----------------------------------- */
.diagram-container {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin: 1.25rem 0;
  box-shadow: var(--shadow);
}
canvas.lesson-diagram {
  display: block;
  width: 100%;
}
.diagram-controls {
  padding: 0.55rem 1rem;
  border-top: 1px solid var(--border);
  background: var(--bg);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}
.diag-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.28rem 0.7rem;
  font-size: 0.78rem;
  font-family: var(--font);
  cursor: pointer;
  color: var(--text-2);
  transition: all 0.15s;
  line-height: 1.5;
}
.diag-btn:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.diag-btn:disabled { opacity: 0.4; cursor: default; }
.diag-step-indicator {
  font-size: 0.75rem;
  color: var(--muted);
  margin-left: auto;
  font-variant-numeric: tabular-nums;
}

/* Legacy ASCII diagram (kept for any missed replacements) */
.diagram {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  margin: 1rem 0;
  font-family: var(--mono);
  font-size: 0.8rem;
  line-height: 1.6;
  overflow-x: auto;
  white-space: pre;
}
.diagram pre { background: none; padding: 0; color: inherit; box-shadow: none; font-size: inherit; }

/* Misc */
mark { background: #fef9c3; padding: 0.05em 0.2em; border-radius: 2px; }

/* --- Responsive ------------------------------------------- */
@media (max-width: 640px) {
  :root { --page-w: 100%; }
  .topbar-inner { padding: 0.6rem 1rem; }
  .home-wrap { padding: 1.25rem 1rem 3rem; }
  .progress-hero { padding: 1.25rem 1.25rem; }
  .hero-pct { font-size: 2.25rem; }
  .days-grid { grid-template-columns: 1fr; }
  .lesson-wrap { padding: 1.5rem 1rem 6rem; }
  .lesson-wrap h1 { font-size: 1.5rem; }
  .lesson-footer { padding: 0.6rem 1rem; }
  .nav-btn { font-size: 0.8rem; padding: 0.4rem 0.7rem; }
  .hero-actions { flex-direction: row; }
}