/* ============================================
   ChalkSheet — style.css
   Design: Scientific Editorial / Warm Precision
   ============================================ */

:root {
  /* Colour palette */
  --slate-950: #0c0e14;
  --slate-900: #151821;
  --slate-800: #1e2233;
  --slate-600: #4a5068;
  --slate-400: #8b92a8;
  --slate-200: #d1d5e0;
  --slate-100: #eceef3;
  --slate-50:  #f6f7fa;
  --chalk:     #faf9f6;
  --amber-500: #d4913a;
  --amber-400: #e5a84b;
  --amber-300: #f0c06e;
  --coral-500: #c9503e;
  --teal-600:  #2a8a7a;
  --teal-500:  #34a793;

  /* Subject colours (content-level tags, shared with print) */
  --physics:   #2c5aa0;
  --chemistry: #2a7a4b;
  --cs:        #b35c00;
  --maths:     #7b4ba0;

  /* Typography */
  --font-display: 'Georgia', 'Times New Roman', 'Palatino Linotype', serif;
  --font-body: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  --font-mono: 'SFMono-Regular', 'Menlo', 'Consolas', 'Liberation Mono', monospace;

  /* Spacing scale */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2.5rem;
  --space-2xl: 4rem;
  --space-3xl: 6rem;

  /* Layout */
  --max-width: 56rem;
  --header-height: 3.5rem;
}

/* ---- Reset ---- */

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

html {
  font-size: 100%;
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.65;
  color: var(--slate-900);
  background-color: var(--chalk);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, svg {
  display: block;
  max-width: 100%;
}

a {
  color: var(--teal-600);
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
  transition: color 0.15s ease;
}

a:hover {
  color: var(--teal-500);
}

a:focus-visible {
  outline: 2px solid var(--amber-500);
  outline-offset: 2px;
}

.hero-cta:focus-visible {
  outline: 2px solid var(--amber-400);
  outline-offset: 2px;
}

/* ---- Layout ---- */

.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

/* ---- Header ---- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  display: flex;
  align-items: center;
  background: var(--slate-950);
  border-bottom: 1px solid var(--slate-800);
}

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

.site-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  text-decoration: none;
  color: var(--chalk);
}

.site-logo-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.75rem;
  height: 1.75rem;
  background: var(--amber-500);
  border-radius: 4px;
  font-family: var(--font-display);
  font-size: 1rem;
  font-weight: 700;
  color: var(--slate-950);
  line-height: 1;
}

.site-logo-text {
  font-family: var(--font-display);
  font-size: 1.1rem;
  font-weight: 400;
  letter-spacing: -0.01em;
  color: var(--chalk);
}

.site-logo-text strong {
  font-weight: 700;
}

.site-nav {
  display: flex;
  gap: var(--space-lg);
  list-style: none;
}

.site-nav a {
  font-size: 0.85rem;
  color: var(--slate-400);
  text-decoration: none;
  letter-spacing: 0.02em;
  transition: color 0.15s ease;
}

.site-nav a:hover,
.site-nav a[aria-current="page"] {
  color: var(--chalk);
}

/* ---- Hero ---- */

.hero {
  padding: var(--space-3xl) 0;
  text-align: center;
  background:
    radial-gradient(ellipse at 20% 80%, rgba(42, 138, 122, 0.06) 0%, transparent 60%),
    radial-gradient(ellipse at 80% 20%, rgba(212, 145, 58, 0.05) 0%, transparent 60%),
    var(--chalk);
}

.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(2rem, 5vw, 3.2rem);
  font-weight: 400;
  line-height: 1.2;
  color: var(--slate-950);
  margin-bottom: var(--space-lg);
}

.hero h1 em {
  font-style: italic;
  color: var(--teal-600);
}

.hero-subtitle {
  font-size: 1.15rem;
  color: var(--slate-600);
  max-width: 34rem;
  margin: 0 auto var(--space-xl);
  line-height: 1.6;
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 0.75rem 1.75rem;
  background: var(--slate-950);
  color: var(--chalk);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 500;
  border-radius: 6px;
  transition: background 0.2s ease, transform 0.15s ease;
}

.hero-cta:hover {
  background: var(--slate-800);
  color: var(--chalk);
  transform: translateY(-1px);
}

.hero-cta svg {
  width: 1rem;
  height: 1rem;
  transition: transform 0.2s ease;
}

.hero-cta:hover svg {
  transform: translateX(3px);
}

/* ---- Simulation cards ---- */

.sim-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(17rem, 1fr));
  gap: var(--space-lg);
  padding: var(--space-2xl) 0;
}

.sim-card {
  background: #fff;
  border: 1px solid var(--slate-200);
  border-radius: 8px;
  padding: var(--space-lg);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.2s ease, box-shadow 0.2s ease, transform 0.15s ease;
}

.sim-card:hover {
  border-color: var(--teal-500);
  box-shadow: 0 4px 20px rgba(42, 138, 122, 0.1);
  transform: translateY(-2px);
  color: inherit;
}

.sim-card-tag {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--amber-500);
  margin-bottom: var(--space-sm);
}

.sim-card-tag[data-subject="physics"]   { color: var(--physics); }
.sim-card-tag[data-subject="chemistry"] { color: var(--chemistry); }
.sim-card-tag[data-subject="cs"]        { color: var(--cs); }
.sim-card-tag[data-subject="maths"]     { color: var(--maths); }

.sim-card h3 {
  font-family: var(--font-display);
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: var(--space-sm);
  line-height: 1.3;
}

.sim-card p {
  font-size: 0.9rem;
  color: var(--slate-600);
  line-height: 1.55;
}

.sim-card-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  margin-top: var(--space-md);
  font-size: 0.75rem;
  color: var(--teal-600);
  font-weight: 500;
}

/* ---- Content pages ---- */

.page-content {
  padding: var(--space-2xl) 0 var(--space-3xl);
}

.page-content h1 {
  font-family: var(--font-display);
  font-size: 2rem;
  font-weight: 400;
  color: var(--slate-950);
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-md);
  border-bottom: 1px solid var(--slate-200);
}

.page-content h2 {
  font-family: var(--font-display);
  font-size: 1.3rem;
  font-weight: 600;
  color: var(--slate-900);
  margin-top: var(--space-xl);
  margin-bottom: var(--space-md);
}

.page-content p {
  margin-bottom: var(--space-md);
  color: var(--slate-800);
}

.page-content ul, .page-content ol {
  padding-left: var(--space-lg);
  margin-bottom: var(--space-md);
}

.page-content li {
  margin-bottom: var(--space-xs);
}

.legal-text {
  font-size: 0.9rem;
  color: var(--slate-600);
  line-height: 1.7;
}

.legal-text h2 {
  font-size: 1.1rem;
}

/* ---- Section headings ---- */

.section-heading {
  text-align: center;
  margin-bottom: var(--space-sm);
}

.section-heading h2 {
  font-family: var(--font-display);
  font-size: 1.6rem;
  font-weight: 400;
  color: var(--slate-950);
}

.section-heading p {
  color: var(--slate-600);
  font-size: 0.95rem;
}

/* ---- Footer ---- */

.site-footer {
  border-top: 1px solid var(--slate-200);
  padding: var(--space-xl) 0;
  margin-top: var(--space-2xl);
}

.site-footer .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-md);
}

.footer-links {
  display: flex;
  gap: var(--space-lg);
  list-style: none;
}

.footer-links a {
  font-size: 0.8rem;
  color: var(--slate-600);
  text-decoration: none;
}

.footer-links a:hover {
  color: var(--slate-900);
}

.footer-copy {
  font-size: 0.8rem;
  color: var(--slate-600);
}

/* ---- Coming soon badge ---- */

.badge-soon {
  display: inline-block;
  font-size: 0.65rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  padding: 0.15rem 0.5rem;
  background: var(--slate-100);
  color: var(--slate-400);
  border-radius: 3px;
  vertical-align: middle;
  margin-left: var(--space-xs);
}

/* ---- Landing page ---- */

.landing {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: calc(100vh - var(--header-height) - 8rem);
  text-align: center;
  padding: var(--space-xl) var(--space-lg);
}

.landing-logo {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.landing-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 3.5rem;
  height: 3.5rem;
  background: var(--amber-500);
  border-radius: 8px;
  font-family: var(--font-display);
  font-size: 2rem;
  font-weight: 700;
  color: var(--slate-950);
  line-height: 1;
}

.landing-text {
  font-family: var(--font-display);
  font-size: 2.2rem;
  font-weight: 400;
  letter-spacing: -0.01em;
  color: var(--slate-950);
}

.landing-text strong {
  font-weight: 700;
}

.landing-tagline {
  font-size: 1.15rem;
  color: var(--slate-600);
  max-width: 28rem;
  line-height: 1.6;
}

/* ---- Responsive ---- */

@media (max-width: 640px) {
  .site-nav {
    gap: var(--space-md);
  }

  .site-nav a {
    font-size: 0.8rem;
  }

  .hero {
    padding: var(--space-2xl) 0;
  }

  .sim-grid {
    grid-template-columns: 1fr;
  }

  .site-footer .container {
    flex-direction: column;
    text-align: center;
  }
}