@font-face {
  font-family: "Product Sans";
  src: local("Product Sans"), local("Google Sans"), local("Google Sans Text");
  font-display: swap;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: var(--text-base);
  line-height: var(--leading-relaxed);
  color: var(--text-primary);
  background:
    radial-gradient(circle at top left, rgba(255,255,255,0.9), transparent 32%),
    radial-gradient(circle at 90% 10%, rgba(234, 240, 255, 0.9), transparent 28%),
    linear-gradient(180deg, #f8f6f1 0%, #f4f1ea 100%);
  min-height: 100vh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image:
    linear-gradient(rgba(255,255,255,0.18) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.18) 1px, transparent 1px);
  background-size: 56px 56px;
  opacity: 0.3;
  z-index: -1;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: var(--font-bold);
  color: var(--text-primary);
  line-height: var(--leading-tight);
  letter-spacing: -0.03em;
}

h1 { font-size: clamp(3rem, 6vw, var(--text-6xl)); }
h2 { font-size: clamp(2.1rem, 4vw, var(--text-4xl)); }
h3 { font-size: clamp(1.5rem, 2.4vw, var(--text-2xl)); }
h4 { font-size: var(--text-lg); }
h5 { font-size: var(--text-base); }
h6 { font-size: var(--text-sm); }

p {
  color: var(--text-secondary);
}

p + p {
  margin-top: var(--space-4);
}

strong, b {
  color: var(--text-primary);
  font-weight: var(--font-semibold);
}

em, i {
  color: var(--text-primary);
}

a {
  color: var(--brand-blue, var(--retro-blue));
  text-decoration: none;
  transition: color var(--transition-fast), opacity var(--transition-fast);
}

a:hover {
  color: var(--brand-blue-deep, var(--retro-blue));
}

ul, ol {
  padding-left: 1.2rem;
  color: var(--text-secondary);
}

li + li {
  margin-top: var(--space-2);
}

ul li::marker,
ol li::marker {
  color: var(--retro-blue);
}

hr {
  border: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, rgba(23, 23, 23, 0.12), transparent);
  margin: var(--space-8) 0;
}

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  padding: 2px 8px;
  border-radius: var(--radius-pill);
  background: var(--bg-surface-soft);
  color: var(--text-primary);
}

pre {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  background: #fff;
  border: var(--border-card);
  border-radius: var(--radius-md);
  padding: var(--space-5);
  overflow: auto;
  box-shadow: var(--shadow-sm);
}

blockquote {
  margin: var(--space-6) 0;
  padding: var(--space-5) var(--space-6);
  border-radius: var(--radius-md);
  background: var(--surface-blue);
  color: var(--text-primary);
  border: 1px solid rgba(111, 131, 247, 0.14);
}

::selection {
  background: rgba(111, 131, 247, 0.18);
  color: var(--text-primary);
}

:focus-visible {
  outline: var(--border-focus);
  outline-offset: 3px;
  border-radius: var(--radius-xs);
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-6) 0;
  background: var(--bg-surface);
  border-radius: var(--radius-md);
  overflow: hidden;
}

th, td {
  text-align: left;
  padding: var(--space-4) var(--space-5);
  border-bottom: var(--border-subtle);
}

th {
  font-size: var(--text-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

canvas,
svg,
video,
iframe,
embed,
object {
  display: block;
  max-width: 100%;
}

canvas,
svg,
video {
  height: auto;
}

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

.container {
  width: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.text-gradient,
.text-gradient-rainbow,
.text-gradient-w1 {
  background: var(--gradient-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.study-content,
.study-content-wrapper {
  max-width: var(--content-max);
}

.study-content h3,
.study-content-wrapper h3 {
  margin: var(--space-8) 0 var(--space-3);
  font-size: clamp(1.45rem, 2vw, 1.9rem);
}

.study-tab-section h3 {
  font-size: clamp(1.4rem, 1.9vw, 1.75rem);
}

.study-content h4,
.study-content-wrapper h4 {
  margin: var(--space-5) 0 var(--space-2);
  font-size: var(--text-sm);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}

.study-content p,
.study-content-wrapper p,
.study-tab-section p,
.practice-content p,
.assignment-content p {
  font-size: 1rem;
  line-height: 1.8;
}

.study-content ul,
.study-content ol,
.study-content-wrapper ul,
.study-content-wrapper ol,
.study-tab-section ul,
.study-tab-section ol,
.practice-content ul,
.practice-content ol,
.assignment-content ul,
.assignment-content ol {
  margin: var(--space-4) 0;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(18px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes pulse-glow {
  0%, 100% { box-shadow: 0 0 0 0 rgba(111, 131, 247, 0); }
  50% { box-shadow: 0 0 0 8px rgba(111, 131, 247, 0.14); }
}

.animate-fade-up {
  animation: fadeUp 0.4s ease both;
}

.animate-fade-in {
  animation: fadeIn 0.3s ease both;
}

@media (max-width: 768px) {
  .container {
    padding: 0 var(--space-4);
  }

  h1 {
    font-size: clamp(2.25rem, 12vw, 3.6rem);
  }
}