/* ============================================================
   Fundamental of X — shared shell styles
   Light manga aesthetic: ink on paper, with one accent.
   ============================================================ */

:root {
  --ink: #1a1a1a;
  --ink-soft: #3a3a3a;
  --ink-faint: #8a8a8a;
  --paper: #f5f1e8;
  --paper-deep: #ede7d6;
  --paper-shadow: #d9d2bd;
  --accent: #d62828;
  --accent-soft: #f4b8b8;
  --hatch: rgba(26, 26, 26, 0.08);
  --radius: 4px;
  --max-content: 1080px;
  --sidebar-w: 260px;
  --font-display: 'Bangers', 'Anton', 'Impact', sans-serif;
  --font-body: 'Inter', 'Source Sans 3', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'Consolas', monospace;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.6;
  /* paper grain texture via tiny radial gradients */
  background-image:
    radial-gradient(circle at 25% 15%, rgba(0,0,0,0.018) 0 1px, transparent 1px),
    radial-gradient(circle at 75% 65%, rgba(0,0,0,0.022) 0 1px, transparent 1px),
    radial-gradient(circle at 45% 85%, rgba(0,0,0,0.015) 0 1px, transparent 1px);
  background-size: 7px 7px, 11px 11px, 13px 13px;
}

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

h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 400;
  letter-spacing: 0.02em;
  color: var(--ink);
  margin: 0 0 0.6em;
  line-height: 1.1;
}

h1 { font-size: clamp(2.4rem, 5vw, 3.6rem); }
h2 { font-size: clamp(1.7rem, 3vw, 2.2rem); }
h3 { font-size: 1.3rem; }

p { margin: 0 0 1em; }

code, pre {
  font-family: var(--font-mono);
  font-size: 0.92em;
}

code {
  background: var(--paper-deep);
  padding: 0.1em 0.35em;
  border-radius: var(--radius);
}

pre {
  background: var(--paper-deep);
  padding: 1em;
  border-radius: var(--radius);
  border: 1.5px solid var(--ink);
  overflow-x: auto;
}

/* =========================
   Page header (site-wide)
   ========================= */
.site-header {
  border-bottom: 2.5px solid var(--ink);
  padding: 1rem 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--paper);
  position: sticky;
  top: 0;
  z-index: 10;
}

.site-header .brand {
  font-family: var(--font-display);
  font-size: 1.6rem;
  letter-spacing: 0.04em;
}

.site-header .brand .accent { color: var(--accent); }

.site-header nav a {
  margin-left: 1.2rem;
  font-size: 0.95rem;
  font-weight: 600;
}

.breadcrumb {
  font-size: 0.85rem;
  color: var(--ink-soft);
  font-family: var(--font-body);
  letter-spacing: 0.02em;
}

.breadcrumb a { color: var(--ink-soft); }
.breadcrumb a:hover { color: var(--accent); }
.breadcrumb .sep { margin: 0 0.4em; color: var(--ink-faint); }
.breadcrumb .current { color: var(--ink); font-weight: 600; }

/* =========================
   Hub grid (subject cards)
   ========================= */
.hub {
  max-width: var(--max-content);
  margin: 3rem auto;
  padding: 0 1.5rem;
}

.hub .intro {
  margin-bottom: 2.5rem;
  max-width: 720px;
}

.hub .intro h1 {
  font-size: clamp(3rem, 7vw, 5rem);
  margin-bottom: 0.3em;
}

.hub .intro h1 .x {
  color: var(--accent);
  display: inline-block;
  transform: rotate(-4deg);
}

.hub .intro p {
  font-size: 1.1rem;
  color: var(--ink-soft);
}

.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.subject-card {
  display: block;
  padding: 1.5rem;
  background: var(--paper);
  border: 2.5px solid var(--ink);
  border-radius: var(--radius);
  position: relative;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
  box-shadow: 4px 4px 0 var(--ink);
}

.subject-card:hover {
  transform: translate(-2px, -2px);
  box-shadow: 6px 6px 0 var(--ink);
  color: var(--ink);
}

.subject-card.coming-soon {
  opacity: 0.5;
  cursor: not-allowed;
  background:
    repeating-linear-gradient(45deg, transparent 0 6px, var(--hatch) 6px 7px),
    var(--paper);
}

.subject-card.coming-soon:hover {
  transform: none;
  box-shadow: 4px 4px 0 var(--ink);
}

.subject-card h3 {
  font-size: 1.8rem;
  margin-bottom: 0.3em;
}

.subject-card h3 .x { color: var(--accent); }

.subject-card .tag {
  position: absolute;
  top: -10px;
  right: -10px;
  background: var(--accent);
  color: white;
  font-family: var(--font-display);
  font-size: 0.85rem;
  letter-spacing: 0.04em;
  padding: 0.2em 0.6em;
  transform: rotate(4deg);
  border: 2px solid var(--ink);
}

.subject-card.coming-soon .tag {
  background: var(--paper-deep);
  color: var(--ink-soft);
}

.subject-card .meta {
  font-size: 0.85rem;
  color: var(--ink-soft);
  margin-top: 0.5rem;
}

/* =========================
   Layout: sidebar + main
   ========================= */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  min-height: calc(100vh - 70px);
}

.sidebar {
  border-right: 2px solid var(--ink);
  padding: 1.5rem 0;
  background: var(--paper-deep);
  position: sticky;
  top: 70px;
  height: calc(100vh - 70px);
  overflow-y: auto;
}

.sidebar h4 {
  font-family: var(--font-display);
  font-size: 1rem;
  letter-spacing: 0.06em;
  padding: 0 1.2rem 0.4rem;
  margin: 0;
  color: var(--ink-soft);
  text-transform: uppercase;
}

.sidebar ol {
  list-style: none;
  padding: 0;
  margin: 0 0 1.5rem;
  counter-reset: lesson;
}

.sidebar ol li {
  counter-increment: lesson;
}

.sidebar ol li a {
  display: block;
  padding: 0.6rem 1.2rem;
  font-size: 0.95rem;
  color: var(--ink);
  border-left: 3px solid transparent;
  transition: background 0.1s ease, border-left-color 0.1s ease;
  position: relative;
}

.sidebar ol li a::before {
  content: counter(lesson, decimal-leading-zero);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--ink-faint);
  margin-right: 0.8em;
}

.sidebar ol li a:hover {
  background: var(--paper-shadow);
  color: var(--ink);
}

.sidebar ol li a.active {
  background: var(--paper);
  border-left-color: var(--accent);
  font-weight: 600;
}

.sidebar ol li a.active::before {
  color: var(--accent);
}

.main {
  padding: 2rem clamp(1.5rem, 4vw, 3rem);
  max-width: 100%;
  overflow-x: hidden;
}

.main > .container {
  max-width: 820px;
  margin: 0 auto;
}

/* =========================
   Lesson layout
   ========================= */
.lesson-header {
  margin-bottom: 2rem;
  padding-bottom: 1rem;
  border-bottom: 2px solid var(--ink);
}

.lesson-header .lesson-num {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent);
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.lesson-header h1 {
  margin: 0.2em 0 0.2em;
}

.lesson-header .blurb {
  color: var(--ink-soft);
  font-size: 1.05rem;
  max-width: 640px;
}

.section {
  margin: 2.5rem 0;
}

.section h2 {
  margin-bottom: 0.6em;
  position: relative;
  display: inline-block;
}

.section h2::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: -4px;
  width: 100%;
  height: 4px;
  background: var(--accent);
  transform: skew(-12deg);
}

.takeaways {
  background: var(--paper-deep);
  border: 2px solid var(--ink);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 2rem 0 1rem;
  box-shadow: 4px 4px 0 var(--ink);
}

.takeaways h3 {
  font-family: var(--font-display);
  font-size: 1.3rem;
  letter-spacing: 0.04em;
  margin: 0 0 0.5rem;
  color: var(--accent);
}

.takeaways ul {
  margin: 0;
  padding-left: 1.2rem;
}

.takeaways li {
  margin: 0.4em 0;
}

/* prev/next lesson nav */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin: 3rem 0 1rem;
  gap: 1rem;
  border-top: 2px solid var(--ink);
  padding-top: 1.5rem;
}

.lesson-nav a {
  flex: 1;
  padding: 1rem 1.25rem;
  border: 2px solid var(--ink);
  border-radius: var(--radius);
  background: var(--paper);
  box-shadow: 3px 3px 0 var(--ink);
  transition: transform 0.12s ease, box-shadow 0.12s ease;
}

.lesson-nav a:hover {
  transform: translate(-2px, -2px);
  box-shadow: 5px 5px 0 var(--ink);
  color: var(--ink);
}

.lesson-nav a.next { text-align: right; }
.lesson-nav .dir {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--ink-faint);
  letter-spacing: 0.1em;
  text-transform: uppercase;
}
.lesson-nav .title {
  font-family: var(--font-display);
  font-size: 1.1rem;
  letter-spacing: 0.02em;
  margin-top: 0.2em;
}
.lesson-nav a.disabled {
  opacity: 0.35;
  pointer-events: none;
}

/* =========================
   Mobile menu / responsive
   ========================= */
.menu-toggle {
  display: none;
  background: none;
  border: 2px solid var(--ink);
  font-family: var(--font-display);
  font-size: 1rem;
  padding: 0.3em 0.7em;
  border-radius: var(--radius);
  cursor: pointer;
}

@media (max-width: 768px) {
  .layout {
    grid-template-columns: 1fr;
  }
  .sidebar {
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    height: auto;
    max-height: calc(100vh - 70px);
    border-right: none;
    border-bottom: 2px solid var(--ink);
    transform: translateY(-110%);
    transition: transform 0.25s ease;
    z-index: 9;
  }
  .sidebar.open {
    transform: translateY(0);
  }
  .menu-toggle {
    display: inline-block;
  }
  .hub .intro h1 {
    font-size: 2.4rem;
  }
}

/* =========================
   Mascot — X-sensei
   ========================= */
.mascot { display: inline-block; vertical-align: middle; overflow: visible; }

.mascot-brand {
  display: inline-block;
  margin-right: 0.6rem;
  vertical-align: middle;
  transform: translateY(-2px);
}

.mascot-hello {
  display: flex;
  align-items: flex-end;
  gap: 1rem;
  margin-top: 1.75rem;
  max-width: 540px;
}

.mascot-hello-figure {
  flex-shrink: 0;
  line-height: 0;
}

.mascot-hello-bubble {
  position: relative;
  background: var(--paper);
  border: 2.5px solid var(--ink);
  border-radius: var(--radius);
  padding: 0.75rem 1rem;
  box-shadow: 4px 4px 0 var(--ink);
  font-size: 0.95rem;
  line-height: 1.45;
}

/* Speech bubble tail pointing to the mascot's head. */
.mascot-hello-bubble::before,
.mascot-hello-bubble::after {
  content: '';
  position: absolute;
  left: -14px;
  top: 18px;
  width: 0;
  height: 0;
  border: 7px solid transparent;
  border-right-color: var(--ink);
}
.mascot-hello-bubble::after {
  left: -10px;
  border-right-color: var(--paper);
}

/* Key Takeaways: mascot pokes in from the top-right corner of the box. */
.takeaways { position: relative; overflow: visible; }

.mascot-takeaway {
  position: absolute;
  top: -38px;
  right: -16px;
  line-height: 0;
  pointer-events: none;
  transform: rotate(6deg);
  z-index: 2;
}

@media (max-width: 768px) {
  .mascot-hello { flex-direction: column; align-items: flex-start; }
  .mascot-hello-bubble::before,
  .mascot-hello-bubble::after { display: none; }
  .mascot-takeaway { display: none; }
}

/* =========================
   Buy Me a Coffee (tip jar)
   ========================= */
.bmc-footer-wrap {
  margin-top: 0.8rem;
  text-align: center;
}

.bmc-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--accent);
  color: white;
  border: 2.5px solid var(--ink);
  border-radius: var(--radius);
  padding: 0.45em 1em;
  font-family: var(--font-display);
  font-size: 1rem;
  letter-spacing: 0.04em;
  box-shadow: 4px 4px 0 var(--ink);
  text-decoration: none;
  transition: transform 0.12s ease, box-shadow 0.12s ease;
}

.bmc-btn:hover {
  transform: translate(-2px, -2px);
  box-shadow: 6px 6px 0 var(--ink);
  color: white;
}

.bmc-btn:active {
  transform: translate(2px, 2px);
  box-shadow: 1px 1px 0 var(--ink);
}

.bmc-btn .bmc-cup {
  font-size: 1.15em;
  line-height: 1;
}

.bmc-card {
  display: flex;
  align-items: center;
  gap: 1rem;
  background: var(--paper);
  border: 2.5px solid var(--ink);
  border-radius: var(--radius);
  padding: 0.85rem 1.1rem;
  box-shadow: 4px 4px 0 var(--ink);
  text-decoration: none;
  color: var(--ink);
  margin: 1.25rem 0 0;
  transition: transform 0.12s ease, box-shadow 0.12s ease;
}

.bmc-card:hover {
  transform: translate(-2px, -2px);
  box-shadow: 6px 6px 0 var(--ink);
  color: var(--ink);
}

.bmc-card-mascot {
  flex-shrink: 0;
  line-height: 0;
}

.bmc-card-text {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.bmc-card-text strong {
  font-family: var(--font-display);
  letter-spacing: 0.04em;
  font-size: 1.2rem;
  color: var(--ink);
}

.bmc-card-text span {
  font-size: 0.9rem;
  color: var(--ink-soft);
  margin-top: 0.15rem;
}

.bmc-card-cta {
  flex-shrink: 0;
  background: var(--accent);
  color: white;
  font-family: var(--font-display);
  letter-spacing: 0.04em;
  font-size: 1rem;
  padding: 0.4em 0.9em;
  border: 2px solid var(--ink);
  border-radius: var(--radius);
  align-self: center;
}

@media (max-width: 540px) {
  .bmc-card { flex-direction: column; text-align: center; }
  .bmc-card-text { align-items: center; }
}

/* =========================
   Footer
   ========================= */
.site-footer {
  border-top: 2px solid var(--ink);
  padding: 1.5rem;
  text-align: center;
  font-size: 0.85rem;
  color: var(--ink-soft);
  margin-top: 3rem;
}