:root {
  --bg: #0a0e14;
  --bg-gradient: radial-gradient(
      ellipse 80% 50% at 50% -10%,
      rgba(96, 165, 250, 0.12),
      transparent 60%
    ),
    radial-gradient(
      ellipse 60% 40% at 90% 10%,
      rgba(249, 115, 22, 0.08),
      transparent 60%
    );
  --surface: #131820;
  --surface-elevated: #1a212c;
  --surface-hover: #1f2733;
  --border: #232b38;
  --border-strong: #2f3a4a;
  --text: #e6edf3;
  --text-muted: #8b95a7;
  --text-dim: #5a6478;

  --zone-easy: #4ade80;
  --zone-tempo: #60a5fa;
  --zone-threshold: #fbbf24;
  --zone-vma: #f97316;
  --zone-sprint: #ef4444;

  --font-sans: "Inter", system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;

  --radius: 14px;
  --radius-lg: 20px;
  --shadow-card: 0 1px 0 rgba(255, 255, 255, 0.03) inset,
    0 10px 30px -15px rgba(0, 0, 0, 0.6);

  --max-width: 1200px;
  --gutter: clamp(20px, 4vw, 48px);
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg);
  background-image: var(--bg-gradient);
  background-attachment: fixed;
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

h1,
h2,
h3 {
  margin: 0;
  letter-spacing: -0.02em;
  line-height: 1.15;
}

p {
  margin: 0;
}

a {
  color: inherit;
}

/* ---------- SITE NAV ---------- */

.site-nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

.site-nav__inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 14px var(--gutter);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.site-nav__brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 15px;
  letter-spacing: -0.01em;
  color: var(--text);
  text-decoration: none;
}

.site-nav__brand-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: linear-gradient(
    135deg,
    var(--zone-easy),
    var(--zone-tempo) 40%,
    var(--zone-sprint)
  );
}

.site-nav__links {
  display: flex;
  align-items: center;
  gap: 4px;
}

.site-nav__link {
  padding: 8px 14px;
  border-radius: 99px;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-muted);
  text-decoration: none;
  transition: color 0.2s ease, background-color 0.2s ease;
}

.site-nav__link:hover {
  color: var(--text);
  background: var(--surface);
}

.site-nav__link[aria-current="page"] {
  color: var(--text);
  background: var(--surface-elevated);
}

/* ---------- BUTTON ---------- */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 12px 22px;
  border-radius: 99px;
  border: 1px solid var(--border-strong);
  background: var(--surface);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 15px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: border-color 0.2s ease, background-color 0.2s ease,
    transform 0.2s ease;
}

.btn:hover {
  border-color: var(--border-strong);
  background: var(--surface-hover);
  transform: translateY(-2px);
}

.btn:focus-visible {
  outline: none;
  border-color: var(--zone-tempo);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--zone-tempo) 25%, transparent);
}

.btn--primary {
  border-color: transparent;
  background: var(--zone-tempo);
  color: #06121f;
}

.btn--primary:hover {
  background: color-mix(in srgb, var(--zone-tempo) 88%, white);
}

/* ---------- HERO ---------- */

.hero {
  padding: clamp(80px, 12vw, 140px) var(--gutter) clamp(60px, 8vw, 100px);
  max-width: var(--max-width);
  margin: 0 auto;
}

.hero__inner {
  animation: fadeUp 0.8s ease-out both;
}

.hero__eyebrow {
  font-size: 13px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.18em;
  color: var(--text-muted);
  margin-bottom: 24px;
}

.hero__title {
  font-size: clamp(48px, 9vw, 112px);
  font-weight: 800;
  letter-spacing: -0.04em;
}

.hero__title-accent {
  background: linear-gradient(
    100deg,
    var(--zone-easy),
    var(--zone-tempo) 35%,
    var(--zone-threshold) 65%,
    var(--zone-sprint)
  );
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
}

.hero__subtitle {
  max-width: 620px;
  font-size: clamp(16px, 1.4vw, 19px);
  color: var(--text-muted);
  margin-top: 24px;
}

/* ---------- SECTIONS ---------- */

.section {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: clamp(48px, 7vw, 96px) var(--gutter);
}

.section__header {
  margin-bottom: 40px;
  max-width: 720px;
}

.section__title {
  font-size: clamp(28px, 3.4vw, 44px);
  font-weight: 700;
}

.section__subtitle {
  margin-top: 12px;
  color: var(--text-muted);
  font-size: clamp(15px, 1.2vw, 17px);
}

/* ---------- TOGGLE ---------- */

.toggle {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  margin-top: 20px;
  padding: 8px 16px 8px 8px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 99px;
  color: var(--text-muted);
  font-family: var(--font-sans);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: border-color 0.2s ease, color 0.2s ease, background-color 0.2s ease;
}

.toggle:hover {
  border-color: var(--border-strong);
  color: var(--text);
}

.toggle:focus-visible {
  outline: none;
  border-color: var(--zone-tempo);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--zone-tempo) 25%, transparent);
}

.toggle__switch {
  position: relative;
  width: 36px;
  height: 20px;
  border-radius: 99px;
  background: var(--border);
  transition: background-color 0.2s ease;
  flex-shrink: 0;
}

.toggle__knob {
  position: absolute;
  top: 2px;
  left: 2px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--text-muted);
  transition: transform 0.2s ease, background-color 0.2s ease;
}

.toggle[aria-pressed="true"] {
  color: var(--text);
  background: color-mix(in srgb, var(--zone-tempo) 12%, var(--surface));
  border-color: color-mix(in srgb, var(--zone-tempo) 35%, var(--border));
}

.toggle[aria-pressed="true"] .toggle__switch {
  background: var(--zone-tempo);
}

.toggle[aria-pressed="true"] .toggle__knob {
  transform: translateX(16px);
  background: #fff;
}

/* ---------- INTRO ---------- */

.intro-grid {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

@media (min-width: 640px) {
  .intro-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1024px) {
  .intro-grid {
    grid-template-columns: repeat(4, 1fr);
  }
}

.intro-item {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 22px 20px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  position: relative;
  transition: border-color 0.2s ease, transform 0.2s ease;
}

.intro-item::before {
  content: "";
  position: absolute;
  top: 0;
  left: 22px;
  right: 22px;
  height: 2px;
  background: linear-gradient(
    90deg,
    var(--zone-easy),
    var(--zone-tempo),
    var(--zone-threshold),
    var(--zone-vma),
    var(--zone-sprint)
  );
  opacity: 0.4;
  border-radius: 0 0 2px 2px;
}

.intro-item:hover {
  border-color: var(--border-strong);
  transform: translateY(-2px);
}

.intro-item__value {
  font-family: var(--font-mono);
  font-size: 30px;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.01em;
  line-height: 1.1;
}

.intro-item__unit {
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: 6px;
}

.intro-item__arrow {
  color: var(--text-dim);
  font-weight: 400;
  margin: 0 2px;
}

.intro-item__label {
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-muted);
}

.intro-item__desc {
  font-size: 14px;
  color: var(--text-muted);
  line-height: 1.5;
}

/* ---------- SPECTRUM ---------- */

.section--spectrum {
  padding-top: clamp(24px, 4vw, 48px);
}

.spectrum {
  position: relative;
  margin: 0;
  padding: 32px 0 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
}

.spectrum__svg {
  width: 100%;
  height: 160px;
  display: block;
  overflow: visible;
}

.spectrum__axis {
  stroke: var(--border-strong);
  stroke-width: 2;
  stroke-linecap: round;
}

.spectrum__point {
  cursor: pointer;
  outline: none;
}

.spectrum__point .spectrum__range {
  transition: opacity 0.2s ease;
}

.spectrum__point .spectrum__dot {
  transition: r 0.2s ease;
}

.spectrum__point:hover .spectrum__range,
.spectrum__point:focus .spectrum__range {
  opacity: 0.7;
}

.spectrum__point:hover .spectrum__dot,
.spectrum__point:focus .spectrum__dot {
  r: 7;
}

.spectrum__labels {
  display: flex;
  justify-content: space-between;
  padding: 0 32px;
  font-size: 12px;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  font-weight: 600;
}

.spectrum__tooltip {
  position: absolute;
  display: flex;
  flex-direction: column;
  gap: 2px;
  background: var(--surface-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 10px;
  padding: 10px 14px;
  font-size: 13px;
  white-space: nowrap;
  pointer-events: none;
  transform: translate(-50%, -100%);
  z-index: 10;
  box-shadow: 0 12px 30px -10px rgba(0, 0, 0, 0.6);
}

.spectrum__tooltip[hidden] {
  display: none;
}

.spectrum__tooltip strong {
  font-weight: 600;
  font-size: 13px;
  color: var(--text);
}

.spectrum__tooltip span {
  color: var(--text-muted);
  font-family: var(--font-mono);
  font-size: 12px;
}

/* ---------- CARDS ---------- */

.cards {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

@media (min-width: 640px) {
  .cards {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1024px) {
  .cards {
    grid-template-columns: repeat(3, 1fr);
  }
}

.card {
  position: relative;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  transition: transform 0.25s ease, border-color 0.25s ease,
    box-shadow 0.25s ease, background-color 0.25s ease;
  overflow: hidden;
  isolation: isolate;
}

.card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(
    circle at top right,
    var(--card-color, transparent),
    transparent 60%
  );
  opacity: 0;
  transition: opacity 0.3s ease;
  pointer-events: none;
  z-index: -1;
}

.card:hover {
  transform: translateY(-3px);
  border-color: var(--card-color, var(--border-strong));
  background: var(--surface-hover);
  box-shadow: 0 20px 40px -20px rgba(0, 0, 0, 0.6),
    0 0 0 1px var(--card-color, transparent) inset;
}

.card:hover::before {
  opacity: 0.1;
}

.card__zone-bar {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--card-color, var(--border));
  opacity: 0.8;
}

.card__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.card__name {
  font-size: 17px;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.card__tag {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--card-color, var(--text-muted));
  background: color-mix(in srgb, var(--card-color, transparent) 12%, transparent);
  padding: 4px 10px;
  border-radius: 99px;
  white-space: nowrap;
}

.card__pace {
  font-family: var(--font-mono);
  font-size: clamp(36px, 4.5vw, 48px);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1;
  color: var(--text);
}

.card__pace-unit {
  font-size: 14px;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: 6px;
  font-family: var(--font-sans);
}

.card__range {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--text-muted);
  padding: 8px 12px;
  background: color-mix(in srgb, var(--card-color, var(--border)) 8%, transparent);
  border: 1px solid color-mix(in srgb, var(--card-color, var(--border)) 25%, transparent);
  border-radius: 99px;
  align-self: flex-start;
}

.card__range-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--card-color, var(--text-muted));
  flex-shrink: 0;
}

.card__range-value {
  font-weight: 600;
  color: var(--text);
}

.card__range-sep {
  color: var(--text-dim);
  font-weight: 400;
}

.card__range-unit {
  font-family: var(--font-sans);
  font-size: 12px;
  color: var(--text-dim);
}

.card__meta {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  font-size: 13px;
  color: var(--text-muted);
}

.card__meta-item {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.card__meta-label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-dim);
  font-weight: 600;
}

.card__meta-value {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--text);
  font-weight: 500;
}

.card__race {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 8px 12px;
  padding: 14px 16px;
  background: color-mix(in srgb, var(--card-color, var(--border)) 8%, transparent);
  border: 1px solid color-mix(in srgb, var(--card-color, var(--border)) 22%, transparent);
  border-radius: 12px;
}

.card__race-label {
  flex-basis: 100%;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-dim);
}

.card__race-value {
  font-family: var(--font-mono);
  font-size: 22px;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.01em;
}

.card__race-range {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--text-muted);
}

.card__race-sep {
  color: var(--text-dim);
  margin: 0 2px;
}

.card__description {
  font-size: 14px;
  color: var(--text-muted);
  line-height: 1.5;
}

/* ---------- CALCULATOR ---------- */

.section--calculator {
  padding-bottom: clamp(80px, 10vw, 120px);
}

.calculator {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: clamp(24px, 3vw, 36px);
  display: grid;
  grid-template-columns: 1fr;
  gap: 20px;
  box-shadow: var(--shadow-card);
}

@media (min-width: 768px) {
  .calculator {
    grid-template-columns: 1fr 1fr 1.4fr;
    align-items: end;
  }
}

.calculator__field {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.calculator__field label {
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-muted);
}

.calculator__field select,
.calculator__field input {
  background: var(--bg);
  border: 1px solid var(--border-strong);
  border-radius: 10px;
  padding: 12px 14px;
  color: var(--text);
  font-family: var(--font-mono);
  font-size: 15px;
  font-weight: 500;
  transition: border-color 0.2s ease, background-color 0.2s ease;
  width: 100%;
}

.calculator__field select:focus,
.calculator__field input:focus {
  outline: none;
  border-color: var(--zone-tempo);
  background: var(--surface);
}

.calculator__result {
  background: var(--surface-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 12px;
  padding: 18px 22px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.calculator__result-label {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-muted);
}

.calculator__result-value {
  font-family: var(--font-mono);
  font-size: clamp(28px, 3vw, 36px);
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--text);
}

.calculator__result-meta {
  font-size: 12px;
  color: var(--text-dim);
  font-family: var(--font-mono);
}

/* ---------- FOOTER ---------- */

.footer {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px var(--gutter) 56px;
  font-size: 13px;
  color: var(--text-dim);
  text-align: center;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.footer__date time {
  font-family: var(--font-mono);
  color: var(--text-muted);
}

/* ---------- CHART ---------- */

.chart {
  position: relative;
  margin: 0;
  padding: 24px clamp(12px, 2vw, 24px) 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
}

.chart__svg {
  width: 100%;
  height: auto;
  display: block;
  overflow: visible;
}

.chart__grid-line {
  stroke: var(--border);
  stroke-width: 1;
}

.chart__grid-label {
  fill: var(--text-dim);
  font-family: var(--font-mono);
  font-size: 11px;
}

.chart__week-label {
  fill: var(--text-dim);
  font-family: var(--font-mono);
  font-size: 11px;
}

.chart__bar {
  cursor: pointer;
  outline: none;
}

.chart__bar-total {
  fill: color-mix(in srgb, var(--bar-color, var(--zone-tempo)) 18%, transparent);
  stroke: color-mix(in srgb, var(--bar-color, var(--zone-tempo)) 55%, transparent);
  stroke-width: 1.5;
  transition: fill 0.2s ease;
}

.chart__bar-long {
  fill: var(--bar-color, var(--zone-tempo));
  transition: opacity 0.2s ease;
}

.chart__bar:hover .chart__bar-total,
.chart__bar:focus .chart__bar-total {
  fill: color-mix(in srgb, var(--bar-color, var(--zone-tempo)) 30%, transparent);
}

.chart__flag {
  fill: var(--text-muted);
  font-size: 11px;
  font-family: var(--font-sans);
}

.chart__phase-bar {
  opacity: 0.85;
}

.chart__phase-label {
  font-family: var(--font-sans);
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.chart__line {
  fill: none;
  stroke: var(--zone-tempo);
  stroke-width: 2.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.chart__dot {
  fill: var(--bar-color, var(--zone-tempo));
  stroke: var(--surface);
  stroke-width: 2;
  cursor: pointer;
  outline: none;
  transition: r 0.2s ease;
}

.chart__dot:hover,
.chart__dot:focus {
  r: 7;
}

.chart__legend {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  padding: 16px 8px 4px;
}

.chart__legend-item {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--text-muted);
}

.chart__legend-dot {
  width: 12px;
  height: 12px;
  border-radius: 3px;
  flex-shrink: 0;
}

.chart__tooltip {
  position: absolute;
  display: flex;
  flex-direction: column;
  gap: 2px;
  background: var(--surface-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 10px;
  padding: 10px 14px;
  font-size: 13px;
  white-space: nowrap;
  pointer-events: none;
  transform: translate(-50%, -100%);
  z-index: 10;
  box-shadow: 0 12px 30px -10px rgba(0, 0, 0, 0.6);
}

.chart__tooltip[hidden] {
  display: none;
}

.chart__tooltip strong {
  font-weight: 600;
  color: var(--text);
}

.chart__tooltip span {
  color: var(--text-muted);
  font-family: var(--font-mono);
  font-size: 12px;
}

.chart__tooltip-change.is-down {
  color: var(--zone-sprint);
}

.chart__down {
  color: var(--zone-sprint);
  font-family: var(--font-mono);
}

/* ---------- NAV HUB (landing) ---------- */

.nav-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
}

.nav-card {
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding: 32px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.25s ease, background 0.25s ease,
    transform 0.25s ease;
}

.nav-card:hover {
  background: var(--surface-hover);
  border-color: var(--border-strong);
  transform: translateY(-3px);
}

.nav-card--soon {
  pointer-events: none;
  opacity: 0.55;
}

.nav-card__tag {
  align-self: flex-start;
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-dim);
  padding: 4px 10px;
  border: 1px solid var(--border);
  border-radius: 99px;
}

.nav-card__title {
  font-size: 24px;
  font-weight: 700;
}

.nav-card__desc {
  color: var(--text-muted);
  font-size: 15px;
}

.nav-card__cta {
  margin-top: 4px;
  font-weight: 600;
  color: var(--zone-tempo);
}

/* ---------- ANIMATIONS ---------- */

@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

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

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}