/* ── Theme tokens (dark default) ── */
:root,
[data-theme="dark"] {
  color-scheme: dark;
  --bg:           #0a0a0f;
  --bg2:          #111118;
  --bg3:          #18181f;
  --surface:      #1e1e28;
  --border:       rgba(255, 255, 255, 0.07);
  --text:         #e8e8f0;
  --muted:        #7a7a8c;
  --accent:       #00e5ff;
  --accent-hover: #33ecff;
  --accent2:      #bf5af2;
  --orange:       #ff6b35;
  --nav-bg:       rgba(10, 10, 15, 0.88);
  --nav-bg-solid: rgba(10, 10, 15, 0.97);
  --hero-grid:    rgba(0, 229, 255, 0.03);
  --glow-cyan:    rgba(0, 229, 255, 0.07);
  --glow-purple:  rgba(191, 90, 242, 0.05);
  --glow-section-cyan:    rgba(0, 229, 255, 0.06);
  --glow-section-purple:  rgba(191, 90, 242, 0.05);
  --noise-opacity: 0.4;
  --overlay:      rgba(10, 10, 15, 0.55);
  --thumb-overlay: rgba(0, 0, 0, 0.5);
  --focus-ring:   rgba(0, 229, 255, 0.12);
  --btn-glow:     rgba(0, 229, 255, 0.35);
  --btn-glow-soft:rgba(0, 229, 255, 0.15);
  --toast-bg:     rgba(0, 229, 255, 0.08);
  --toast-border: rgba(0, 229, 255, 0.25);
  --card-shadow:  rgba(0, 0, 0, 0.45);
  --label-accent-bg:  rgba(0, 229, 255, 0.1);
  --label-accent-bd:  rgba(0, 229, 255, 0.22);
  --label-accent2-bg: rgba(191, 90, 242, 0.1);
  --label-accent2-bd: rgba(191, 90, 242, 0.22);
  --label-orange-bg:  rgba(255, 107, 53, 0.1);
  --label-orange-bd:  rgba(255, 107, 53, 0.22);
  --thumb-fade-end:   rgba(17, 17, 24, 0.95);
}

[data-theme="light"] {
  color-scheme: light;
  --bg:           #f4f5f9;
  --bg2:          #ffffff;
  --bg3:          #eef0f6;
  --surface:      #e2e6ef;
  --border:       rgba(0, 0, 0, 0.09);
  --text:         #12121a;
  --muted:        #5a5a6e;
  --accent:       #007f9a;
  --accent-hover: #00a3c4;
  --accent2:      #8b3fc7;
  --orange:       #d94e1a;
  --nav-bg:       rgba(244, 245, 249, 0.9);
  --nav-bg-solid: rgba(255, 255, 255, 0.98);
  --hero-grid:    rgba(0, 127, 154, 0.08);
  --glow-cyan:    rgba(0, 127, 154, 0.1);
  --glow-purple:  rgba(139, 63, 199, 0.07);
  --glow-section-cyan:    rgba(0, 127, 154, 0.08);
  --glow-section-purple:  rgba(139, 63, 199, 0.06);
  --noise-opacity: 0.2;
  --overlay:      rgba(244, 245, 249, 0.72);
  --thumb-overlay: rgba(255, 255, 255, 0.65);
  --focus-ring:   rgba(0, 127, 154, 0.18);
  --btn-glow:     rgba(0, 127, 154, 0.28);
  --btn-glow-soft:rgba(0, 127, 154, 0.12);
  --toast-bg:     rgba(0, 127, 154, 0.08);
  --toast-border: rgba(0, 127, 154, 0.22);
  --card-shadow:  rgba(0, 0, 0, 0.1);
  --label-accent-bg:  rgba(0, 127, 154, 0.1);
  --label-accent-bd:  rgba(0, 127, 154, 0.25);
  --label-accent2-bg: rgba(139, 63, 199, 0.1);
  --label-accent2-bd: rgba(139, 63, 199, 0.25);
  --label-orange-bg:  rgba(217, 78, 26, 0.1);
  --label-orange-bd:  rgba(217, 78, 26, 0.25);
  --thumb-fade-end:   rgba(255, 255, 255, 0.92);
}

/* ── Smooth motion tokens ── */
:root {
  --ease-smooth: cubic-bezier(0.22, 1, 0.36, 1);
  --ease-out:    cubic-bezier(0.16, 1, 0.3, 1);
  --ease-spring: cubic-bezier(0.34, 1.15, 0.64, 1);
  --t-fast:  0.4s;
  --t-med:   0.55s;
  --t-slow:  0.8s;
}

html.theme-switching,
html.theme-switching *,
html.theme-switching *::before,
html.theme-switching *::after {
  transition:
    background-color var(--t-med) var(--ease-smooth),
    color var(--t-med) var(--ease-smooth),
    border-color var(--t-med) var(--ease-smooth),
    fill var(--t-med) var(--ease-smooth),
    stroke var(--t-med) var(--ease-smooth),
    box-shadow var(--t-med) var(--ease-smooth) !important;
}

/* ── Theme toggle button ── */
.nav-right {
  display: flex;
  align-items: center;
  gap: 0.65rem;
}
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 38px;
  height: 38px;
  padding: 0;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg3);
  color: var(--text);
  cursor: pointer;
  flex-shrink: 0;
  transition:
    transform var(--t-fast) var(--ease-spring),
    border-color var(--t-fast) var(--ease-smooth),
    background var(--t-fast) var(--ease-smooth),
    color var(--t-fast) var(--ease-smooth);
}
.theme-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
  transform: scale(1.06);
}
.theme-toggle:active { transform: scale(0.96); }
.theme-toggle svg {
  width: 18px;
  height: 18px;
  transition: transform var(--t-med) var(--ease-spring), opacity var(--t-fast) ease;
}
.theme-toggle .icon-moon { display: none; }
[data-theme="light"] .theme-toggle .icon-sun { display: none; }
[data-theme="light"] .theme-toggle .icon-moon { display: block; }

/* ── Skip link ── */
.skip-link {
  position: absolute;
  top: -100%;
  left: 1rem;
  z-index: 10000;
  padding: 0.6rem 1rem;
  background: var(--accent);
  color: var(--bg);
  font-family: var(--mono);
  font-size: 0.75rem;
  border-radius: 0 0 8px 8px;
  transition: top var(--t-fast) var(--ease-smooth);
}
.skip-link:focus {
  top: 0;
  outline: 2px solid var(--text);
  outline-offset: 2px;
}

/* ── Scroll progress ── */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 2px;
  width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  z-index: 200;
  pointer-events: none;
  transition: width 0.1s linear;
}

/* ── Nav scroll state ── */
nav.is-scrolled {
  padding-top: 0.85rem;
  padding-bottom: 0.85rem;
  background: var(--nav-bg-solid);
  box-shadow: 0 8px 32px var(--card-shadow);
}

/* ── Back to top ── */
.back-to-top {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 85;
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--nav-bg-solid);
  backdrop-filter: blur(16px);
  color: var(--muted);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition:
    opacity var(--t-fast) var(--ease-smooth),
    transform var(--t-fast) var(--ease-spring),
    visibility var(--t-fast),
    border-color var(--t-fast) var(--ease-smooth),
    color var(--t-fast) var(--ease-smooth);
}
.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: none;
}
.back-to-top:hover {
  border-color: var(--accent);
  color: var(--accent);
  transform: translateY(-3px);
}
.back-to-top svg { width: 18px; height: 18px; }

@media (max-width: 768px) {
  .back-to-top { bottom: 5.5rem; right: 1rem; }
}