html {
  font-family: var(--font-sans);
  font-size: 16px;
  color: var(--color-text);
  background: var(--color-bg);
}

body {
  font-size: var(--fs-base);
  font-weight: var(--fw-regular);
  color: var(--color-text);
  background: var(--color-bg);
}

h1,
h2,
h3,
h4 {
  font-weight: var(--fw-semibold);
  letter-spacing: -0.02em;
  color: var(--color-text);
}

h1 {
  font-size: var(--fs-5xl);
  font-weight: var(--fw-bold);
}

h2 {
  font-size: var(--fs-4xl);
}

h3 {
  font-size: var(--fs-2xl);
}

h4 {
  font-size: var(--fs-xl);
}

a {
  color: inherit;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary);
}

/* Layout primitives */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--container-px);
}

.section {
  padding-block: var(--section-py);
}

/* Section eyebrow tag (small uppercase label above headings) */
.eyebrow {
  display: inline-block;
  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-primary);
}

/* Generic muted body text */
.muted {
  color: var(--color-text-muted);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: 0.75rem 1.25rem;
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  line-height: 1;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: background-color var(--transition-base),
              color var(--transition-base),
              border-color var(--transition-base),
              box-shadow var(--transition-base),
              transform var(--transition-fast);
  white-space: nowrap;
}

.btn:active {
  transform: translateY(1px);
}

.btn-primary {
  background: var(--color-primary);
  color: var(--color-on-dark);
  box-shadow: 0 1px 2px rgba(15, 17, 21, 0.08), 0 2px 6px rgba(43, 108, 238, 0.2);
}

.btn-primary:hover {
  background: var(--color-primary-hover);
  color: var(--color-on-dark);
  box-shadow: 0 2px 4px rgba(15, 17, 21, 0.1), 0 4px 12px rgba(43, 108, 238, 0.28);
}

.btn-secondary {
  background: var(--color-bg);
  color: var(--color-text);
  border-color: var(--color-border-strong);
}

.btn-secondary:hover {
  background: var(--color-surface);
  color: var(--color-text);
}

.btn-dark {
  background: var(--color-dark);
  color: var(--color-on-dark);
}

.btn-dark:hover {
  background: var(--color-dark-2);
  color: var(--color-on-dark);
}

/* === Scroll-driven fade-in ===
   Tiny IntersectionObserver script in index.html toggles `.is-visible`. */

.fade-in-on-scroll {
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.7s ease-out, transform 0.7s ease-out;
  will-change: opacity, transform;
}

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

@media (prefers-reduced-motion: reduce) {
  .fade-in-on-scroll {
    opacity: 1 !important;
    transform: none !important;
    transition: none !important;
  }
}

/* Visually hidden (for accessible labels) */
.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;
}