:root {
  color-scheme: light dark;
  font-family: "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  font-size: 16px;
  line-height: 1.6;
  --surface: #f7f9fc;
  --surface-alt: #ffffff;
  --surface-muted: rgba(148, 163, 184, 0.08);
  --border: rgba(15, 23, 42, 0.12);
  --border-strong: rgba(37, 99, 235, 0.35);
  --text: #0f172a;
  --muted: #475569;
  --accent: #2563eb;
  --accent-dark: #1d4ed8;
  --accent-contrast: #f8fafc;
  --warning: #f97316;
  --shadow-card: 0 18px 40px rgba(15, 23, 42, 0.16);
  --shadow-float: 0 22px 48px rgba(37, 99, 235, 0.24);
  --focus-ring: rgba(37, 99, 235, 0.45);
}

@media (prefers-color-scheme: dark) {
  :root {
    --surface: #0d1423;
    --surface-alt: #111c33;
    --surface-muted: rgba(59, 130, 246, 0.16);
    --border: rgba(148, 163, 184, 0.22);
    --border-strong: rgba(96, 165, 250, 0.45);
    --text: #e2e8f0;
    --muted: #94a3b8;
    --accent: #7aa8ff;
    --accent-dark: #5c8fff;
    --accent-contrast: #050b18;
    --shadow-card: 0 22px 48px rgba(2, 6, 23, 0.7);
    --shadow-float: 0 26px 56px rgba(37, 99, 235, 0.4);
    --focus-ring: rgba(96, 165, 250, 0.5);
  }
}

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

body {
  margin: 0;
  min-height: 100vh;
  background: var(--surface);
  color: var(--text);
}

a {
  color: inherit;
  text-decoration: none;
}

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

.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;
}

.container {
  width: min(74rem, 95vw);
  margin-inline: auto;
}

.page-header {
  padding: clamp(2.8rem, 5vw, 4.4rem) 0 clamp(2.1rem, 4vw, 3.4rem);
  background: linear-gradient(185deg, rgba(37, 99, 235, 0.18), transparent 70%);
}

.header-actions {
  display: flex;
  justify-content: flex-end;
  margin-bottom: 1.25rem;
}

.home-link {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.45rem 1.1rem;
  border-radius: 999px;
  border: 1px solid rgba(148, 163, 184, 0.32);
  background: rgba(148, 163, 184, 0.18);
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  transition: transform 0.2s ease, background-color 0.2s ease, border-color 0.2s ease, color 0.2s ease;
}

.home-link:hover,
.home-link:focus-visible {
  transform: translateY(-1px);
  background: rgba(191, 219, 254, 0.85);
  border-color: rgba(191, 219, 254, 0.6);
  color: #0f172a;
}

.eyebrow {
  margin: 0 0 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.18em;
  font-size: 0.75rem;
  color: var(--muted);
}

.page-header h1 {
  margin: 0 0 0.85rem;
  font-size: clamp(2.3rem, 5vw, 3.3rem);
  line-height: 1.12;
}

.lede {
  margin: 0;
  max-width: 62ch;
  color: var(--muted);
}

.viewer {
  display: grid;
  gap: clamp(2rem, 5vw, 3rem);
  margin-bottom: clamp(3rem, 6vw, 4.5rem);
}

.viewer__header {
  display: grid;
  gap: 0.85rem;
}

.section-eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.22em;
  font-size: 0.72rem;
  color: var(--muted);
  margin: 0;
}

.section-title {
  margin: 0;
  font-size: clamp(1.9rem, 3.6vw, 2.4rem);
  line-height: 1.2;
}

.section-lede {
  margin: 0;
  max-width: 60ch;
  color: var(--muted);
}

.viewer {
  grid-template-columns: minmax(0, 2fr);
}

.viewer__panel {
  display: grid;
  gap: 1.5rem;
  grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr));
}

.panel-card {
  background: var(--surface-alt);
  border-radius: 1.25rem;
  border: 1px solid var(--border);
  box-shadow: var(--shadow-card);
  padding: clamp(1.4rem, 3vw, 1.9rem);
  display: grid;
  gap: 1rem;
}

.panel-card h3 {
  margin: 0;
  font-size: 1.15rem;
}

.hint-list {
  margin: 0;
  padding-left: 1.25rem;
  display: grid;
  gap: 0.75rem;
  color: var(--muted);
}

.hint-list li {
  margin: 0;
}

.hint-key {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2rem;
  padding: 0.15rem 0.6rem;
  border-radius: 0.6rem;
  border: 1px solid rgba(148, 163, 184, 0.45);
  background: rgba(148, 163, 184, 0.2);
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  margin-right: 0.35rem;
}

.viewer-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 0.6rem 1.25rem;
  border-radius: 999px;
  border: 1px solid rgba(148, 163, 184, 0.4);
  background: rgba(148, 163, 184, 0.18);
  font-weight: 600;
  letter-spacing: 0.04em;
  cursor: pointer;
  transition: transform 0.2s ease, background-color 0.2s ease, border-color 0.2s ease, color 0.2s ease;
}

.btn.icon {
  min-width: 6.5rem;
}

.btn:hover,
.btn:focus-visible {
  transform: translateY(-2px);
  background: rgba(37, 99, 235, 0.22);
  border-color: rgba(96, 165, 250, 0.45);
  color: var(--text);
}

.btn.ghost {
  background: rgba(148, 163, 184, 0.12);
}

.viewer-scale {
  margin: 0;
  font-weight: 600;
  color: var(--muted);
}

.viewer__stage {
  border-radius: 1.5rem;
  border: 1px solid var(--border);
  overflow: hidden;
  background: linear-gradient(135deg, rgba(148, 163, 184, 0.18), rgba(191, 219, 254, 0.16));
  box-shadow: var(--shadow-card);
}

.viewer-canvas {
  position: relative;
  width: 100%;
  padding-top: min(60%, 32rem);
  overflow: hidden;
  touch-action: none;
  cursor: grab;
  transition: box-shadow 0.2s ease;
}

.viewer-canvas.is-panning {
  cursor: grabbing;
  box-shadow: var(--shadow-float);
}

.viewer-viewport {
  position: absolute;
  inset: 0;
  transform-origin: top left;
  transition: transform 0.08s linear;
}

.viewer-viewport svg {
  display: block;
  width: 100%;
  height: 100%;
  user-select: none;
}

.viewer-tooltip {
  position: absolute;
  top: calc(var(--tooltip-top, 0px));
  left: calc(var(--tooltip-left, 0px));
  transform: translate(-50%, -110%);
  background: rgba(15, 23, 42, 0.92);
  color: #f8fafc;
  border-radius: 1rem;
  border: 1px solid rgba(96, 165, 250, 0.45);
  padding: 0.85rem 1rem;
  box-shadow: 0 20px 48px rgba(15, 23, 42, 0.5);
  max-width: min(18rem, 70vw);
  pointer-events: none;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.18s ease, visibility 0.18s ease, transform 0.18s ease;
}

.viewer-tooltip.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translate(-50%, -120%);
}

.viewer-tooltip.is-flip {
  transform: translate(-50%, 20%);
}

.viewer-tooltip.is-flip.is-visible {
  transform: translate(-50%, 10%);
}

.tooltip-title {
  margin: 0 0 0.35rem;
  font-weight: 700;
  letter-spacing: 0.04em;
}

.tooltip-body {
  margin: 0;
  font-size: 0.95rem;
}

.pid-grid .grid-line {
  stroke: rgba(148, 163, 184, 0.25);
  stroke-width: 1;
}

.pid-piping path {
  fill: none;
  stroke: url(#pipe-gradient);
  stroke-width: 36;
  stroke-linejoin: round;
  stroke-linecap: round;
}

.pid-labels text {
  font-size: 20px;
  fill: var(--muted);
  text-anchor: start;
}

.pid-component {
  cursor: pointer;
  transition: filter 0.18s ease, transform 0.18s ease;
  outline: none;
}

.pid-component .component-code {
  font-size: 20px;
  text-anchor: middle;
  fill: var(--muted);
}

.pid-component.pump .pump-body {
  fill: rgba(37, 99, 235, 0.15);
  stroke: var(--accent);
  stroke-width: 6;
}

.pid-component.pump .pump-impeller {
  fill: rgba(37, 99, 235, 0.55);
}

.pid-component.pump .pump-arrow {
  stroke: var(--accent-dark);
  stroke-width: 6;
  stroke-linecap: round;
  stroke-linejoin: round;
  fill: none;
}

.pid-component.valve .valve-body {
  fill: rgba(59, 130, 246, 0.2);
  stroke: var(--accent);
  stroke-width: 4;
}

.pid-component.valve .valve-stem {
  fill: rgba(59, 130, 246, 0.35);
}

.pid-component.exchanger .hx-shell {
  fill: rgba(14, 165, 233, 0.18);
  stroke: rgba(14, 165, 233, 0.6);
  stroke-width: 6;
}

.pid-component.exchanger .hx-core {
  fill: url(#heat-exchanger);
  stroke: rgba(14, 165, 233, 0.65);
  stroke-width: 4;
}

.pid-component.exchanger .hx-tube {
  stroke: rgba(14, 165, 233, 0.7);
  stroke-width: 4;
}

.pid-component:focus-visible,
.pid-component:hover {
  filter: drop-shadow(0 0 16px rgba(37, 99, 235, 0.45));
}

.pid-component.is-active {
  filter: drop-shadow(0 0 24px rgba(37, 99, 235, 0.6));
  transform: translateY(-2px);
}

.viewer-canvas:not(.is-panning) .pid-component:focus-visible {
  transform: translateY(-1px);
}

.back-to-top {
  position: fixed;
  right: clamp(1rem, 4vw, 2.5rem);
  bottom: clamp(1.4rem, 4vw, 2.8rem);
  padding: 0.75rem 1.8rem;
  border-radius: 999px;
  background: rgba(15, 23, 42, 0.85);
  color: #f8fafc;
  border: 1px solid rgba(148, 163, 184, 0.45);
  box-shadow: 0 18px 36px rgba(15, 23, 42, 0.35);
  backdrop-filter: blur(12px);
  letter-spacing: 0.06em;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity 0.25s ease, visibility 0.25s ease, background-color 0.2s ease, border-color 0.2s ease,
    transform 0.2s ease;
}

.back-to-top::before {
  content: "\2191";
  font-size: 1.05rem;
  line-height: 1;
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  animation: backToTopPulse 6s ease-in-out infinite;
}

.back-to-top:hover,
.back-to-top:focus-visible {
  transform: translateY(-4px);
  background: rgba(37, 99, 235, 0.85);
  border-color: rgba(96, 165, 250, 0.5);
  color: #f8fafc;
}

.footer {
  padding: clamp(2.4rem, 4vw, 3.4rem) 0;
}

.footer-actions {
  display: flex;
  justify-content: center;
}

@keyframes backToTopPulse {

  0%,
  100% {
    box-shadow: 0 18px 36px rgba(15, 23, 42, 0.35);
  }

  50% {
    box-shadow: 0 22px 44px rgba(37, 99, 235, 0.28);
  }
}

@media (max-width: 62rem) {
  .viewer__panel {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 48rem) {
  .header-actions {
    justify-content: flex-start;
  }

  .viewer-canvas {
    padding-top: min(80%, 28rem);
  }

  .viewer-controls {
    justify-content: stretch;
  }

  .btn {
    flex: 1 1 auto;
  }
}

@media (prefers-reduced-motion: reduce) {

  *,
  *::before,
  *::after {
    animation: none !important;
    transition: none !important;
  }
}