/* ==========================================================================
   VIPERA — Stylesheet
   Design tokens: Emerald #10B981 · Electric Blue #2563EB · Cyan #06B6D4 ·
                  Gold #F5B942 · Ink #0B1220 · Bright aurora-on-white surface
   Type: Outfit (display) · Inter (UI) · JetBrains Mono (data/score)
   ========================================================================== */

:root {
  /* --- Color tokens --- */
  --emerald: #10B981;
  --emerald-dark: #059669;
  --blue: #2563EB;
  --cyan: #06B6D4;
  --gold: #F5B942;
  --gold-dark: #E0A527;
  --ink: #0B1220;
  --ink-soft: #445066;
  --danger: #EF4444;

  --bg-base: #F3FBF8;
  --surface: #FFFFFF;
  --surface-glass: rgba(255, 255, 255, 0.62);
  --surface-glass-strong: rgba(255, 255, 255, 0.82);
  --border-glass: rgba(15, 23, 42, 0.08);

  --grad-brand: linear-gradient(135deg, var(--emerald) 0%, var(--cyan) 55%, var(--blue) 100%);
  --grad-gold: linear-gradient(135deg, #FFDE8A 0%, var(--gold) 100%);

  /* --- Elevation --- */
  --shadow-sm: 0 2px 8px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 10px 30px rgba(15, 23, 42, 0.10);
  --shadow-lg: 0 24px 60px rgba(15, 23, 42, 0.14);
  --shadow-glow-emerald: 0 8px 28px rgba(16, 185, 129, 0.35);

  /* --- Radii --- */
  --r-sm: 10px;
  --r-md: 16px;
  --r-lg: 24px;
  --r-xl: 32px;
  --r-pill: 999px;

  /* --- Type --- */
  --font-display: 'Outfit', system-ui, sans-serif;
  --font-body: 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', monospace;

  /* --- Motion --- */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --dur-fast: 150ms;
  --dur-med: 300ms;
  --dur-slow: 600ms;

  color-scheme: light;
}

@media (prefers-reduced-motion: reduce) {
  :root { --dur-fast: 0ms; --dur-med: 0ms; --dur-slow: 0ms; }
}

/* ==========================================================================
   Reset
   ========================================================================== */

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body, h1, h2, h3, p, fieldset, legend, figure { margin: 0; padding: 0; }
ul { list-style: none; margin: 0; padding: 0; }
button { font: inherit; color: inherit; background: none; border: none; cursor: pointer; }
input { font: inherit; }
svg { display: block; }
img { max-width: 100%; display: block; }

@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;
  }
}

html, body {
  height: 100%;
  overscroll-behavior: none;
}

body {
  font-family: var(--font-body);
  background: var(--bg-base);
  color: var(--ink);
  min-height: 100vh;
  min-height: 100dvh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* Focus visibility — accessible, on-brand ring */
:focus-visible {
  outline: 2.5px solid var(--blue);
  outline-offset: 3px;
  border-radius: var(--r-sm);
}

.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;
}

.skip-link {
  position: absolute;
  left: 12px; top: -60px;
  background: var(--ink);
  color: #fff;
  padding: 10px 16px;
  border-radius: var(--r-sm);
  z-index: 1000;
  transition: top var(--dur-fast) var(--ease-out);
}
.skip-link:focus { top: 12px; }

/* ==========================================================================
   Ambient background: aurora blobs + particle canvas
   ========================================================================== */

.aurora {
  position: fixed;
  inset: 0;
  z-index: -2;
  overflow: hidden;
  pointer-events: none;
}

.aurora__blob {
  position: absolute;
  border-radius: 50%;
  filter: blur(70px);
  opacity: 0.5;
  will-change: transform;
}

.aurora__blob--emerald {
  width: 46vw; height: 46vw;
  top: -12vw; left: -10vw;
  background: radial-gradient(circle, var(--emerald) 0%, transparent 70%);
  animation: driftA 22s ease-in-out infinite alternate;
}
.aurora__blob--blue {
  width: 40vw; height: 40vw;
  bottom: -15vw; right: -8vw;
  background: radial-gradient(circle, var(--blue) 0%, transparent 70%);
  animation: driftB 26s ease-in-out infinite alternate;
}
.aurora__blob--cyan {
  width: 34vw; height: 34vw;
  top: 30vh; right: 20vw;
  background: radial-gradient(circle, var(--cyan) 0%, transparent 70%);
  opacity: 0.35;
  animation: driftC 30s ease-in-out infinite alternate;
}

@keyframes driftA { from { transform: translate(0,0) scale(1); } to { transform: translate(6vw, 8vh) scale(1.12); } }
@keyframes driftB { from { transform: translate(0,0) scale(1); } to { transform: translate(-8vw, -6vh) scale(1.08); } }
@keyframes driftC { from { transform: translate(0,0) scale(1); } to { transform: translate(4vw, -10vh) scale(0.94); } }

.particles-canvas {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  width: 100%;
  height: 100%;
}

/* ==========================================================================
   Glass utility
   ========================================================================== */

.glass {
  background: var(--surface-glass);
  backdrop-filter: blur(18px) saturate(160%);
  -webkit-backdrop-filter: blur(18px) saturate(160%);
  border: 1px solid var(--border-glass);
  box-shadow: var(--shadow-md);
}

/* ==========================================================================
   Top bar
   ========================================================================== */

.topbar {
  position: sticky;
  top: 0;
  z-index: 40;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px clamp(16px, 4vw, 40px);
}

.topbar__brand { display: flex; align-items: center; gap: 10px; }
.topbar__logo { border-radius: 9px; box-shadow: var(--shadow-sm); }
.topbar__title {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.25rem;
  letter-spacing: -0.01em;
}

.topbar__actions { display: flex; gap: 8px; }

.icon-btn {
  display: grid;
  place-items: center;
  width: 44px; height: 44px;
  border-radius: var(--r-pill);
  background: var(--surface-glass);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid var(--border-glass);
  color: var(--ink-soft);
  transition: transform var(--dur-fast) var(--ease-out), color var(--dur-fast), box-shadow var(--dur-fast);
}
.icon-btn:hover { color: var(--emerald-dark); box-shadow: var(--shadow-sm); transform: translateY(-1px); }
.icon-btn:active { transform: translateY(0) scale(0.94); }
.icon-btn[aria-pressed="true"] { color: var(--emerald-dark); }
.icon-btn--sm { width: 38px; height: 38px; }
.icon-btn .icon { width: 20px; height: 20px; }

/* ==========================================================================
   Buttons
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 0.98rem;
  padding: 13px 24px;
  border-radius: var(--r-pill);
  transition: transform var(--dur-fast) var(--ease-spring), box-shadow var(--dur-fast), filter var(--dur-fast);
  white-space: nowrap;
}
.btn:active { transform: scale(0.97); }

.btn--primary {
  color: #fff;
  background: var(--grad-brand);
  box-shadow: var(--shadow-glow-emerald);
}
.btn--primary:hover { filter: brightness(1.06); transform: translateY(-2px); }

.btn--xl { padding: 17px 34px; font-size: 1.08rem; }

.btn--ghost {
  color: var(--ink);
  background: var(--surface-glass);
  border: 1px solid var(--border-glass);
  backdrop-filter: blur(10px);
}
.btn--ghost:hover { background: var(--surface-glass-strong); }

.btn--danger-ghost {
  color: var(--danger);
  background: rgba(239, 68, 68, 0.08);
  border: 1px solid rgba(239, 68, 68, 0.25);
}
.btn--danger-ghost:hover { background: rgba(239, 68, 68, 0.14); }

.btn--sm { padding: 9px 16px; font-size: 0.88rem; }

/* ==========================================================================
   Home screen
   ========================================================================== */

.screen { min-height: 100vh; min-height: 100dvh; }

.screen--home {
  display: flex;
  flex-direction: column;
  padding: clamp(8px, 3vw, 24px) clamp(16px, 6vw, 40px) 24px;
}

.home__hero {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  max-width: 780px;
  margin: 0 auto;
  padding-top: clamp(12px, 4vh, 40px);
}

.home__badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--emerald-dark);
  background: rgba(16, 185, 129, 0.10);
  border: 1px solid rgba(16, 185, 129, 0.22);
  padding: 7px 14px;
  border-radius: var(--r-pill);
  margin-bottom: 22px;
  animation: fadeUp var(--dur-slow) var(--ease-out) both;
}
.home__badge-dot {
  width: 7px; height: 7px;
  border-radius: 50%;
  background: var(--gold);
  box-shadow: 0 0 0 4px rgba(245, 185, 66, 0.25);
}

.home__title {
  font-family: var(--font-display);
  font-weight: 800;
  font-size: clamp(3.2rem, 11vw, 6.4rem);
  line-height: 0.95;
  letter-spacing: -0.03em;
  background: var(--grad-brand);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  animation: fadeUp var(--dur-slow) var(--ease-out) 80ms both;
}
.home__title-tail { color: var(--gold); -webkit-text-fill-color: var(--gold); }

.home__tagline {
  font-size: clamp(1rem, 2.4vw, 1.2rem);
  color: var(--ink-soft);
  margin-top: 14px;
  max-width: 46ch;
  animation: fadeUp var(--dur-slow) var(--ease-out) 160ms both;
}

/* Signature: the living snake stage, sits behind/around the CTA */
.hero-stage {
  position: relative;
  width: min(600px, 100%);
  height: 90px;
  margin-top: 8px;
  animation: fadeUp var(--dur-slow) var(--ease-out) 220ms both;
}
.hero-stage__path { position: absolute; inset: 0; width: 100%; height: 100%; opacity: 0; }
.hero-stage__canvas { position: absolute; inset: 0; width: 100%; height: 100%; }

.home__cta-group {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  justify-content: center;
  margin-top: 12px;
  animation: fadeUp var(--dur-slow) var(--ease-out) 280ms both;
}

.difficulty-picker {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-top: 34px;
  border: none;
  animation: fadeUp var(--dur-slow) var(--ease-out) 340ms both;
}
.difficulty-picker__legend {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--ink-soft);
  margin-right: 4px;
}

.chip {
  position: relative;
  cursor: pointer;
}
.chip input {
  position: absolute;
  opacity: 0;
  width: 100%; height: 100%;
  margin: 0;
  cursor: pointer;
}
.chip span {
  display: inline-flex;
  align-items: center;
  padding: 9px 18px;
  border-radius: var(--r-pill);
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--ink-soft);
  background: var(--surface-glass);
  border: 1.5px solid var(--border-glass);
  transition: all var(--dur-fast) var(--ease-out);
}
.chip input:checked + span {
  color: #fff;
  background: var(--grad-brand);
  border-color: transparent;
  box-shadow: var(--shadow-glow-emerald);
}
.chip input:focus-visible + span { outline: 2.5px solid var(--blue); outline-offset: 2px; }
.chip:hover span:not(:has(+ *)) {}
.chip:hover input:not(:checked) + span { background: var(--surface-glass-strong); color: var(--ink); }

.home__stats {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  justify-content: center;
  margin-top: 40px;
  animation: fadeUp var(--dur-slow) var(--ease-out) 400ms both;
}

.stat-card {
  display: flex;
  flex-direction: column;
  gap: 4px;
  min-width: 130px;
  padding: 16px 22px;
  border-radius: var(--r-lg);
}
.stat-card__label {
  font-size: 0.74rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--ink-soft);
}
.stat-card__value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 1.6rem;
  color: var(--ink);
}

.site-footer {
  text-align: center;
  color: var(--ink-soft);
  font-size: 0.78rem;
  padding-top: 40px;
  opacity: 0.8;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(16px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ==========================================================================
   Game screen
   ========================================================================== */

.screen--game {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 12px clamp(12px, 4vw, 32px) 20px;
  gap: 16px;
}

.hud {
  width: 100%;
  max-width: 640px;
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 10px 14px;
  border-radius: var(--r-lg);
}

.hud__scores {
  display: flex;
  align-items: center;
  gap: 14px;
  flex: 1;
  justify-content: center;
}
.hud__score-block { display: flex; flex-direction: column; align-items: center; line-height: 1.1; }
.hud__score-label {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--ink-soft);
}
.hud__score-value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 1.5rem;
  color: var(--emerald-dark);
}
.hud__score-block--muted .hud__score-value { color: var(--ink-soft); font-size: 1.2rem; }
.hud__divider { width: 1px; height: 28px; background: var(--border-glass); }

.hud__badges { display: none; }
@media (min-width: 460px) {
  .hud__badges { display: block; }
}

.badge {
  font-size: 0.72rem;
  font-weight: 700;
  padding: 6px 12px;
  border-radius: var(--r-pill);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.badge--easy { background: rgba(16,185,129,0.14); color: var(--emerald-dark); }
.badge--medium { background: rgba(37,99,235,0.12); color: var(--blue); }
.badge--hard { background: rgba(239,68,68,0.12); color: var(--danger); }

/* Score pop animation when scoring */
.hud__score-value.score-pop { animation: scorePop 340ms var(--ease-spring); }
@keyframes scorePop {
  0% { transform: scale(1); }
  40% { transform: scale(1.35); color: var(--gold-dark); }
  100% { transform: scale(1); }
}

.board-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 18px;
  width: 100%;
  flex: 1;
}

.board {
  position: relative;
  width: min(640px, 92vw);
  aspect-ratio: 1 / 1;
  border-radius: var(--r-xl);
  overflow: hidden;
  padding: 10px;
}

#game-canvas {
  width: 100%;
  height: 100%;
  display: block;
  border-radius: var(--r-lg);
  background:
    radial-gradient(circle at 20% 15%, rgba(16,185,129,0.06), transparent 55%),
    radial-gradient(circle at 85% 85%, rgba(37,99,235,0.06), transparent 55%),
    #FBFEFD;
}

.board-overlay {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(243, 251, 248, 0.72);
  backdrop-filter: blur(6px);
  border-radius: var(--r-xl);
  animation: fadeIn var(--dur-med) var(--ease-out) both;
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

.countdown-number {
  font-family: var(--font-display);
  font-weight: 800;
  font-size: 6rem;
  background: var(--grad-brand);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  animation: countPulse 1s var(--ease-spring) both;
}
@keyframes countPulse {
  0% { transform: scale(0.5); opacity: 0; }
  50% { transform: scale(1.15); opacity: 1; }
  100% { transform: scale(1); opacity: 1; }
}

.overlay-panel {
  width: min(340px, 88%);
  border-radius: var(--r-xl);
  padding: 32px 28px;
  text-align: center;
  animation: panelIn var(--dur-med) var(--ease-spring) both;
}
@keyframes panelIn {
  from { opacity: 0; transform: translateY(14px) scale(0.96); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

.overlay-panel__title {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.7rem;
}
.overlay-panel__title--gameover { color: var(--ink); }
.overlay-panel__subtitle { color: var(--ink-soft); font-size: 0.92rem; margin-top: 6px; }
.overlay-panel__badge {
  display: inline-block;
  margin-top: 10px;
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--gold-dark);
  background: rgba(245, 185, 66, 0.16);
  border: 1px solid rgba(245, 185, 66, 0.35);
  padding: 5px 12px;
  border-radius: var(--r-pill);
  animation: shimmerIn 900ms var(--ease-out);
}
@keyframes shimmerIn { from { transform: translateY(-6px); opacity: 0;} to { transform: translateY(0); opacity: 1; } }

.overlay-panel__score {
  margin: 18px 0 6px;
  display: flex;
  align-items: baseline;
  justify-content: center;
  gap: 8px;
}
.overlay-panel__score-value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 3rem;
  color: var(--emerald-dark);
}
.overlay-panel__score-label { color: var(--ink-soft); font-size: 0.9rem; }

.overlay-panel__actions {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-top: 22px;
}
.overlay-panel__actions .btn { width: 100%; }

/* ==========================================================================
   Touch controls
   ========================================================================== */

.touch-controls {
  display: none;
  justify-content: center;
  padding-bottom: env(safe-area-inset-bottom);
}

@media (hover: none) and (pointer: coarse), (max-width: 720px) {
  .touch-controls { display: flex; }
}

.dpad {
  display: grid;
  grid-template-columns: repeat(3, 58px);
  grid-template-rows: repeat(3, 58px);
  gap: 6px;
}
.dpad__btn {
  border-radius: var(--r-md);
  background: var(--surface-glass);
  backdrop-filter: blur(14px);
  border: 1px solid var(--border-glass);
  color: var(--ink-soft);
  display: grid;
  place-items: center;
  box-shadow: var(--shadow-sm);
  transition: transform 100ms var(--ease-out), background 100ms, color 100ms;
  touch-action: none;
}
.dpad__btn svg { width: 24px; height: 24px; }
.dpad__btn:active { transform: scale(0.9); background: var(--grad-brand); color: #fff; }
.dpad__btn--up { grid-column: 2; grid-row: 1; }
.dpad__btn--left { grid-column: 1; grid-row: 2; }
.dpad__btn--center { grid-column: 2; grid-row: 2; background: transparent; border: none; box-shadow: none; }
.dpad__btn--right { grid-column: 3; grid-row: 2; }
.dpad__btn--down { grid-column: 2; grid-row: 3; }

/* ==========================================================================
   Modals
   ========================================================================== */

.modal-backdrop {
  position: fixed;
  inset: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(11, 18, 32, 0.35);
  backdrop-filter: blur(4px);
  padding: 20px;
  animation: fadeIn var(--dur-fast) var(--ease-out) both;
}

.modal {
  width: min(420px, 100%);
  max-height: 86vh;
  overflow-y: auto;
  border-radius: var(--r-xl);
  background: var(--surface-glass-strong);
  animation: panelIn var(--dur-med) var(--ease-spring) both;
}

.modal__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 22px 14px;
  position: sticky;
  top: 0;
  background: inherit;
  border-radius: var(--r-xl) var(--r-xl) 0 0;
}
.modal__header h2 {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.25rem;
}

.modal__body { padding: 4px 22px 24px; display: flex; flex-direction: column; gap: 4px; }

.setting-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px 0;
  border-bottom: 1px solid var(--border-glass);
}
.setting-row:last-child { border-bottom: none; }
.setting-row__label { display: block; font-weight: 600; font-size: 0.94rem; }
.setting-row__hint { display: block; font-size: 0.78rem; color: var(--ink-soft); margin-top: 2px; }
.setting-row--danger { padding-top: 18px; }

.switch { position: relative; display: inline-block; width: 46px; height: 27px; flex-shrink: 0; }
.switch input { position: absolute; opacity: 0; width: 100%; height: 100%; margin: 0; cursor: pointer; z-index: 1; }
.switch__track {
  position: absolute; inset: 0;
  background: #D9E2E8;
  border-radius: var(--r-pill);
  transition: background var(--dur-fast) var(--ease-out);
}
.switch__thumb {
  position: absolute;
  top: 3px; left: 3px;
  width: 21px; height: 21px;
  background: #fff;
  border-radius: 50%;
  box-shadow: var(--shadow-sm);
  transition: transform var(--dur-fast) var(--ease-spring);
}
.switch input:checked ~ .switch__track { background: var(--grad-brand); }
.switch input:checked ~ .switch__track .switch__thumb { transform: translateX(19px); }
.switch input:focus-visible ~ .switch__track { outline: 2.5px solid var(--blue); outline-offset: 2px; }

.howto-list { display: flex; flex-direction: column; gap: 14px; padding-bottom: 6px; }
.howto-list li { font-size: 0.92rem; line-height: 1.5; color: var(--ink-soft); }
.howto-list strong { color: var(--ink); }

/* ==========================================================================
   Icon show/hide state helpers
   ========================================================================== */
[hidden] { display: none !important; }

/* ==========================================================================
   Responsive tuning
   ========================================================================== */

@media (max-width: 480px) {
  .home__stats { gap: 10px; }
  .stat-card { min-width: 100px; padding: 12px 14px; }
  .stat-card__value { font-size: 1.3rem; }
  .dpad { grid-template-columns: repeat(3, 52px); grid-template-rows: repeat(3, 52px); }
  .overlay-panel { padding: 26px 20px; }
}

@media (min-width: 900px) {
  .board { width: min(640px, 60vh); }
}

@media (min-width: 1200px) {
  .home__hero { max-width: 860px; }
}

/* Landscape phones: keep game screen compact */
@media (max-height: 480px) and (orientation: landscape) {
  .screen--game { flex-direction: row; flex-wrap: wrap; align-items: center; justify-content: center; gap: 10px;}
  .hud { max-width: 220px; flex-direction: column; height: 100%; }
  .board { width: min(70vh, 60vw); }
  .board-wrap { flex-direction: row; }
  .touch-controls { padding-left: 8px; }
}