/* Shared visual system for the educational web app. */

:root {
  color-scheme: light;

  /* Design-system color scale (single source of truth). */
  --blue-950: #071B3A;
  --blue-900: #0A2A5E;
  --blue-800: #0F3B7A;
  --blue-700: #1556B8;
  --blue-600: #2563EB;
  --blue-500: #3B82F6;
  --blue-100: #DBEAFE;
  --blue-075: #EAF2FF;
  --blue-050: #F4F8FF;

  --ink-950: #0F172A;
  --ink-800: #1E293B;
  --ink-600: #475569;

  --border: #D8E2F0;
  --border-blue: #BBD7FF;
  --surface: #FFFFFF;
  --surface-soft: #F8FAFC;

  --green-700: #157347;
  --green-600: #16824F;
  --green-100: #DFF8EA;
  --green-050: #F0FFF6;

  --amber-700: #92400E;
  --amber-100: #FEF3C7;
  --amber-050: #FFFBEB;

  --color-primary: var(--blue-600);
  --color-primary-strong: var(--blue-800);
  --color-primary-deep: var(--blue-950);
  --color-primary-soft: #eef4ff;
  --color-secondary: #60a5fa;
  --color-secondary-soft: #dbeafe;
  --color-accent: #93c5fd;
  --color-accent-soft: #eff6ff;
  --color-success: #1d4ed8;
  --color-warning: #1e40af;
  --color-error: #1e3a8a;
  --color-background: #f7f9fc;
  --color-background-strong: #e8edf6;
  --color-surface: var(--surface);
  --color-surface-glass: rgba(255, 255, 255, .82);
  --color-border: var(--border);
  --color-border-strong: rgba(15, 23, 42, .18);
  --color-text: var(--ink-950);
  --color-text-soft: var(--ink-800);
  --color-muted: var(--ink-600);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 22px;
  --shadow-soft: 0 10px 26px rgba(15, 23, 42, .07);
  --shadow-card: 0 18px 48px rgba(15, 23, 42, .11);
  --shadow-lift: 0 26px 72px rgba(15, 23, 42, .18);
  --transition-fast: 160ms ease;
  --transition-base: 240ms ease;

  /* Typography roles: Fraunces for big titles, Cormorant Garamond for
     badges/buttons/tabs/labels, Inter for body text and inputs. */
  --font-heading: "Fraunces", Georgia, serif;
  --font-accent: "Cormorant Garamond", Georgia, serif;
  --font-body: "Inter", "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  --font-main: var(--font-body);
  --font-display: var(--font-heading);
  --font-ui: var(--font-accent);

  /* Backwards-compatible tokens used by existing page CSS. */
  --c-ink: var(--color-text);
  --c-ink-2: var(--color-text-soft);
  --c-bg: var(--color-background);
  --c-card: var(--color-surface);
  --c-muted: var(--color-muted);
  --c-brand: var(--color-primary-strong);
  --c-brand-2: var(--color-primary);
  --c-accent: var(--color-secondary);
  --shadow: var(--shadow-soft);
  --shadow-inset: inset 0 0 0 1px var(--color-border);
  --shadow-lg: var(--shadow-card);
  --radius: var(--radius-lg);
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-main);
  color: var(--color-text);
  line-height: 1.6;
  background:
    linear-gradient(180deg, rgba(37, 99, 235, .08), transparent 420px),
    radial-gradient(circle at 12% 16%, rgba(96, 165, 250, .12), transparent 28rem),
    radial-gradient(circle at 88% 8%, rgba(30, 64, 175, .08), transparent 24rem),
    var(--color-background);
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background-image:
    linear-gradient(rgba(15, 23, 42, .045) 1px, transparent 1px),
    linear-gradient(90deg, rgba(15, 23, 42, .045) 1px, transparent 1px);
  background-size: 44px 44px;
  mask-image: linear-gradient(to bottom, rgba(0,0,0,.7), transparent 68%);
}

a { color: inherit; }

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

button, input, select, textarea {
  font: inherit;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible {
  outline: 3px solid rgba(11, 92, 255, .24);
  outline-offset: 2px;
}

.site-header {
  position: relative;
  overflow: hidden;
  color: #fff;
  padding: clamp(3.5rem, 8vw, 6rem) 1.25rem clamp(2.6rem, 6vw, 4.25rem);
  background:
    linear-gradient(135deg, rgba(15, 23, 42, .96), rgba(30, 58, 138, .94) 55%, rgba(37, 99, 235, .88)),
    url("data:image/svg+xml,%3Csvg width='1200' height='620' viewBox='0 0 1200 620' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' stroke='rgba(255,255,255,0.16)' stroke-width='2'%3E%3Cpath d='M80 470 C260 260 420 520 620 300 S970 170 1120 360'/%3E%3Cpath d='M140 210 C330 120 430 250 580 180 S870 30 1050 150'/%3E%3C/g%3E%3Cg fill='rgba(255,255,255,0.22)'%3E%3Ccircle cx='190' cy='210' r='5'/%3E%3Ccircle cx='456' cy='312' r='4'/%3E%3Ccircle cx='790' cy='198' r='6'/%3E%3Ccircle cx='1010' cy='340' r='5'/%3E%3C/g%3E%3C/svg%3E");
  background-size: cover;
  background-position: center;
}

.site-header::after {
  content: "";
  position: absolute;
  left: 50%;
  bottom: -92px;
  width: min(960px, 92vw);
  height: 180px;
  transform: translateX(-50%);
  border-radius: 999px;
  background: rgba(255,255,255,.18);
  filter: blur(28px);
}

.site-header h1,
.site-header p {
  position: relative;
  z-index: 1;
  max-width: 980px;
  margin-left: auto;
  margin-right: auto;
  text-align: center;
}

.site-header h1 {
  margin-top: 0;
  margin-bottom: .9rem;
  font-family: var(--font-display);
  font-size: clamp(2.25rem, 4vw, 4.5rem);
  line-height: 1;
  font-weight: 800;
}

.site-header p {
  margin-top: 0;
  margin-bottom: 0;
  color: rgba(255, 255, 255, .84);
  font-size: clamp(1rem, 1.8vw, 1.22rem);
}

.topnav {
  position: sticky;
  top: .75rem;
  z-index: 200;
  width: min(1180px, calc(100% - 1.5rem));
  margin: .75rem auto 0;
  border: 1px solid rgba(255,255,255,.7);
  border-radius: 18px;
  background: rgba(255, 255, 255, .78);
  backdrop-filter: blur(18px);
  box-shadow: 0 12px 28px rgba(15, 23, 42, .06);
}

.topnav-inner {
  max-width: 1180px;
  margin: 0 auto;
  padding: .62rem .7rem;
  display: flex;
  align-items: center;
  gap: .7rem;
}

.nav-left {
  display: inline-flex;
  align-items: center;
  gap: .58rem;
  min-width: 0;
  color: var(--color-text);
  font-weight: 850;
  letter-spacing: 0;
  white-space: nowrap;
}

.nav-left::before {
  content: "";
  width: 34px;
  height: 34px;
  border-radius: 10px;
  background:
    linear-gradient(135deg, var(--color-primary), var(--color-secondary));
  box-shadow: 0 10px 22px rgba(11, 92, 255, .24);
}

h1,
h2,
h3,
h4,
.nav-left {
  font-family: var(--font-display);
}

button,
.tab,
.subtab {
  font-family: var(--font-accent);
}

.nav-spacer { flex: 1; }

.nav-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 38px;
  padding: .48rem .84rem;
  border: 1px solid transparent;
  border-radius: 12px;
  color: var(--color-text-soft);
  text-decoration: none;
  font-size: .93rem;
  font-weight: 750;
  white-space: nowrap;
  transition: background var(--transition-fast), color var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast);
}

.nav-link:hover {
  color: var(--color-primary-strong);
  background: rgba(11, 92, 255, .08);
  border-color: rgba(11, 92, 255, .14);
  transform: translateY(-1px);
}

.nav-link.active {
  color: #fff;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-strong));
  box-shadow: 0 12px 24px rgba(11, 92, 255, .22);
}

.wrap {
  max-width: 1180px;
  margin: 0 auto;
  padding: clamp(1rem, 3vw, 2rem) 1.1rem 4rem;
}

.pill {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  padding: .22rem .62rem;
  border-radius: 999px;
  border: 1px solid rgba(11, 92, 255, .16);
  background: var(--color-primary-soft);
  color: var(--color-primary-strong);
  font-size: .78rem;
  font-weight: 800;
}

.page-footer {
  margin-top: 3rem;
  padding: 2rem 1rem;
  text-align: center;
  color: var(--color-muted);
  border-top: 1px solid var(--color-border);
  background: rgba(255,255,255,.62);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}

.reveal-on-scroll {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 520ms ease, transform 520ms ease;
}

.motion-ui-ready .reveal-on-scroll {
  opacity: 1;
  transform: none;
  transition: none;
}

.reveal-on-scroll.is-visible {
  opacity: 1;
  transform: translateY(0);
}

.animated-page,
.animated-section,
.animated-card,
.animated-chart-container,
.animated-modal,
.animated-button,
.animated-tab {
  will-change: transform, opacity;
}

.animated-card,
.animated-chart-container {
  transition: border-color var(--transition-base), box-shadow var(--transition-base), background var(--transition-base);
}

.animated-card:hover,
.animated-chart-container:hover {
  border-color: rgba(37, 99, 235, .18);
  box-shadow: var(--shadow-card);
}

.animated-button,
.animated-tab {
  transform-origin: center;
}

.motion-reduced *,
.motion-reduced *::before,
.motion-reduced *::after {
  animation-duration: 1ms !important;
  animation-iteration-count: 1 !important;
  scroll-behavior: auto !important;
  transition-duration: 1ms !important;
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 1ms !important;
    animation-iteration-count: 1 !important;
    scroll-behavior: auto !important;
    transition-duration: 1ms !important;
  }
}

@media (max-width: 760px) {
  .topnav {
    top: .4rem;
    width: calc(100% - .8rem);
    border-radius: 14px;
  }

  .topnav-inner {
    overflow-x: auto;
    padding: .62rem .8rem;
    scrollbar-width: none;
  }

  .topnav-inner::-webkit-scrollbar { display: none; }
  .nav-spacer { display: none; }
  .nav-link { flex: 0 0 auto; }
  .site-header { padding-top: 3rem; }
}

/* ============== Reusable design-system primitives ============== */

.formula-box,
.math-box {
  background: linear-gradient(180deg, var(--blue-050), #FFFFFF);
  border: 1px solid var(--border-blue);
  border-radius: 14px;
  padding: 24px;
  color: var(--blue-900);
  text-align: center;
}

.btn-warning,
button.warning {
  background: var(--amber-050);
  color: var(--amber-700);
  border: 1px solid var(--amber-100);
  border-radius: 14px;
  font-family: var(--font-accent);
  font-weight: 700;
}

.solution-step {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--surface-soft);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px 18px;
}

.step-number {
  background: var(--blue-600);
  color: white;
  width: 34px;
  height: 34px;
  border-radius: 999px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-ui);
  font-weight: 800;
}