/* ─────────────────────────────────────────────
   Mathblog – Minimalist Modern CSS
   ───────────────────────────────────────────── */

:root {
  --clr-bg:        #0f1117;
  --clr-surface:   #1a1d27;
  --clr-border:    #2e3248;
  --clr-accent:    #7c6af7;
  --clr-accent-lt: #a99ef9;
  --clr-text:      #e4e6f0;
  --clr-muted:     #8589a3;
  --font-sans:     'Inter', system-ui, -apple-system, sans-serif;
  --font-mono:     'Fira Code', 'Cascadia Code', monospace;
  --radius:        10px;
  --max-w:         720px;
}

/* ── Reset ────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  background-color: var(--clr-bg);
  color: var(--clr-text);
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.75;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ── Layout ───────────────────────────────── */
.container {
  width: 100%;
  max-width: var(--max-w);
  margin-inline: auto;
  padding-inline: 1.5rem;
}

main { flex: 1; padding-block: 4rem 6rem; }

/* ── Site Header ──────────────────────────── */
.site-header {
  border-bottom: 1px solid var(--clr-border);
  padding-block: 1.1rem;
  position: sticky;
  top: 0;
  background: rgba(15, 17, 23, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  z-index: 100;
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.site-logo {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--clr-accent-lt);
  text-decoration: none;
  letter-spacing: -0.02em;
}

/* ── Language Switcher ────────────────────── */
.lang-switcher {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  list-style: none;
}

.lang-switcher li { display: flex; align-items: center; }

.lang-switcher .sep {
  color: var(--clr-border);
  font-size: 0.85rem;
  user-select: none;
}

.lang-switcher a {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--clr-muted);
  text-decoration: none;
  padding: 0.25rem 0.5rem;
  border-radius: 5px;
  transition: color 0.2s, background 0.2s;
}

.lang-switcher a:hover,
.lang-switcher a.active {
  color: var(--clr-accent-lt);
  background: rgba(124, 106, 247, 0.12);
}

/* ── Hero / Intro ─────────────────────────── */
.hero {
  margin-bottom: 3rem;
}

.hero .tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--clr-accent);
  border: 1px solid rgba(124, 106, 247, 0.35);
  border-radius: 20px;
  padding: 0.2rem 0.75rem;
  margin-bottom: 1.1rem;
}

h1 {
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 1rem;
  color: #fff;
}

.lead {
  font-size: 1.05rem;
  color: var(--clr-muted);
  max-width: 60ch;
}

/* ── Equation Card ────────────────────────── */
.equation-card {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 2rem 2.25rem;
  margin-bottom: 2.5rem;
  overflow-x: auto;
}

.equation-card .eq-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--clr-accent);
  margin-bottom: 1rem;
}

.equation-card .math-block {
  font-size: 1.1rem;
  color: #fff;
  margin-block: 0.5rem;
  overflow-x: auto;
}

/* ── Prose / Explanation ──────────────────── */
.explanation h2 {
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: #fff;
  margin-bottom: 0.75rem;
}

.explanation p {
  color: var(--clr-muted);
  margin-bottom: 1rem;
}

.explanation .term {
  color: var(--clr-text);
  font-weight: 600;
}

.terms-grid {
  display: grid;
  gap: 0.6rem;
  margin-top: 1.25rem;
}

.term-row {
  display: grid;
  grid-template-columns: 2.5rem 1fr;
  align-items: baseline;
  gap: 1rem;
  font-size: 0.95rem;
  padding: 0.6rem 1rem;
  background: rgba(255,255,255,0.02);
  border-radius: 6px;
  border-left: 2px solid var(--clr-accent);
}

.term-row .sym {
  color: var(--clr-accent-lt);
  font-family: var(--font-mono);
  font-size: 0.88rem;
  text-align: center;
}

.term-row .desc { color: var(--clr-muted); }

/* ── Footer ───────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--clr-border);
  padding-block: 1.5rem;
  text-align: center;
  font-size: 0.8rem;
  color: var(--clr-muted);
}

/* ── Responsive ───────────────────────────── */
@media (max-width: 480px) {
  .equation-card { padding: 1.25rem; }
  .term-row { grid-template-columns: 1fr; gap: 0.25rem; }
}