:root {
  --bg-top: #8de0ff;
  --bg-mid: #2d89b3;
  --bg-bottom: #06162d;
  --hud-bg: rgba(4, 17, 31, 0.46);
  --hud-border: rgba(190, 242, 255, 0.36);
  --hud-text: #eaffff;
  --accent: #67f2ff;
  --danger: #ff6f67;
  --ok: #7bffbe;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
}

body {
  background:
    radial-gradient(circle at 15% 20%, rgba(128, 231, 255, 0.25), transparent 42%),
    radial-gradient(circle at 85% 80%, rgba(42, 128, 184, 0.35), transparent 46%),
    linear-gradient(180deg, var(--bg-top), var(--bg-mid) 45%, var(--bg-bottom));
  color: var(--hud-text);
  font-family: "Avenir Next", "Century Gothic", "Trebuchet MS", sans-serif;
}

#app {
  position: relative;
  width: 100vw;
  height: 100vh;
}

#game-canvas {
  width: 100%;
  height: 100%;
  display: block;
}

#hud {
  position: absolute;
  top: 1rem;
  left: 1rem;
  right: 1rem;
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 0.75rem;
  pointer-events: none;
  z-index: 5;
}

.hud-block {
  background: var(--hud-bg);
  border: 1px solid var(--hud-border);
  border-radius: 12px;
  padding: 0.5rem 0.75rem;
  backdrop-filter: blur(4px);
  box-shadow: 0 0 0 1px rgba(10, 24, 44, 0.28), 0 6px 20px rgba(0, 8, 18, 0.26);
  min-width: 0;
}

#depth-block {
  justify-self: start;
}

#best-block {
  justify-self: center;
}

#air-block {
  justify-self: end;
  width: min(260px, 34vw);
}

.hud-label {
  display: block;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.82;
}

.hud-value {
  display: block;
  font-size: 1.22rem;
  font-weight: 700;
  text-shadow: 0 1px 0 rgba(0, 0, 0, 0.3);
}

#air-gauge-shell {
  margin-top: 0.28rem;
  width: 100%;
  height: 14px;
  border-radius: 999px;
  background: rgba(14, 28, 46, 0.8);
  overflow: hidden;
  border: 1px solid rgba(161, 229, 245, 0.22);
}

#air-gauge-fill {
  height: 100%;
  width: 100%;
  background: linear-gradient(90deg, #57ffba, #35d6ff);
  transition: width 120ms linear, filter 120ms linear;
}

#air-gauge-fill.critical {
  background: linear-gradient(90deg, #ff7169, #ffb74a);
  filter: saturate(1.25) brightness(1.05);
  animation: pulse-air 0.75s ease-in-out infinite;
}

@keyframes pulse-air {
  0% {
    opacity: 0.95;
  }
  50% {
    opacity: 0.5;
  }
  100% {
    opacity: 0.95;
  }
}

#overlay {
  position: absolute;
  inset: 0;
  display: grid;
  align-content: center;
  justify-items: center;
  text-align: center;
  gap: 0.6rem;
  background: linear-gradient(180deg, rgba(0, 14, 31, 0.2), rgba(0, 7, 17, 0.62));
  color: #f3feff;
  opacity: 0;
  pointer-events: none;
  transform: translateY(1rem);
  transition: opacity 240ms ease, transform 260ms ease;
  z-index: 6;
  padding: 1rem;
}

#overlay.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

#overlay-title {
  margin: 0;
  font-family: "Futura", "Avenir Next", sans-serif;
  font-size: clamp(2rem, 6vw, 4rem);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

#overlay-subtitle,
#overlay-stats {
  margin: 0;
  font-size: clamp(0.95rem, 2.6vw, 1.2rem);
  max-width: min(720px, 92vw);
  opacity: 0.95;
}

#overlay-stats {
  min-height: 1.5em;
  color: var(--accent);
}

#overlay-button {
  margin-top: 0.4rem;
  border: 1px solid rgba(194, 243, 255, 0.72);
  background: linear-gradient(180deg, rgba(18, 65, 104, 0.9), rgba(13, 41, 73, 0.9));
  color: #ecfdff;
  padding: 0.62rem 1.2rem;
  border-radius: 999px;
  font-size: 1rem;
  letter-spacing: 0.04em;
  cursor: pointer;
}

#overlay-button:focus-visible {
  outline: 2px solid #9cf4ff;
  outline-offset: 2px;
}

#overlay a {
  color: #c8f5ff;
  font-size: 0.95rem;
  text-underline-offset: 0.2em;
}

@media (max-width: 720px) {
  #hud {
    top: 0.5rem;
    left: 0.5rem;
    right: 0.5rem;
    gap: 0.5rem;
  }

  .hud-block {
    padding: 0.4rem 0.5rem;
  }

  .hud-label {
    font-size: 0.62rem;
  }

  .hud-value {
    font-size: 1rem;
  }

  #air-block {
    width: min(170px, 40vw);
  }
}

.portal-back {
  position: fixed;
  bottom: 1rem;
  left: 1rem;
  z-index: 100;
  color: #00c8c8;
  font-size: 0.85rem;
  text-decoration: none;
  opacity: 0.7;
  transition: opacity 150ms ease;
}
.portal-back:hover { opacity: 1; }