:root {
  --bg: #0f1115;
  --fg: #eaeaea;
  --accent: #5eb1ff;
  --muted: #9aa0a6;
  --border: #2a2d34;
}

:root[data-theme="light"] {
  --bg: #ffffff;
  --fg: #1a1a1a;
  --accent: #1d6fd6;
  --muted: #5b6168;
  --border: #e1e4e8;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.6;
  transition: background 0.2s, color 0.2s;
}

header {
  position: relative;
}

#theme-toggle {
  position: absolute;
  top: 2rem;
  right: 1.5rem;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 999px;
  width: 2.5rem;
  height: 2.5rem;
  font-size: 1.1rem;
  padding: 0;
  color: var(--fg);
}

#theme-toggle:hover {
  opacity: 0.8;
}

nav {
  display: flex;
  gap: 1rem;
  margin-bottom: 1rem;
}

nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.95rem;
}

nav a:hover,
nav a.active {
  color: var(--accent);
}

header, main, footer {
  max-width: 640px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

header h1 {
  margin-bottom: 0.25rem;
}

header p {
  color: var(--muted);
}

section {
  margin-bottom: 2rem;
}

h2 {
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.4rem;
}

button {
  background: var(--accent);
  color: #06111f;
  border: none;
  padding: 0.6rem 1.2rem;
  border-radius: 6px;
  font-size: 1rem;
  cursor: pointer;
}

button:hover {
  opacity: 0.9;
}

footer {
  color: var(--muted);
  font-size: 0.9rem;
  border-top: 1px solid var(--border);
}

.tank {
  position: relative;
  width: 100%;
  height: 400px;
  overflow: hidden;
  border-radius: 10px;
  background: linear-gradient(to bottom, #1a4d7a, #0a2540);
  border: 4px solid #5c3a1e;
}

.fish {
  position: absolute;
  font-size: 2rem;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

.fish-1 {
  top: 20%;
  animation-name: swim-right;
  animation-duration: 9s;
}

.fish-2 {
  top: 45%;
  animation-name: swim-left;
  animation-duration: 12s;
}

.fish-3 {
  top: 65%;
  animation-name: swim-right;
  animation-duration: 15s;
  animation-delay: -4s;
}

.fish-4 {
  top: 30%;
  animation-name: swim-left;
  animation-duration: 7s;
  animation-delay: -2s;
}

@keyframes swim-right {
  0% { left: -10%; transform: scaleX(-1); }
  49% { transform: scaleX(-1); }
  50% { left: 105%; transform: scaleX(1); }
  99% { transform: scaleX(1); }
  100% { left: -10%; transform: scaleX(-1); }
}

@keyframes swim-left {
  0% { left: 105%; transform: scaleX(1); }
  49% { transform: scaleX(1); }
  50% { left: -10%; transform: scaleX(-1); }
  99% { transform: scaleX(-1); }
  100% { left: 105%; transform: scaleX(1); }
}

.bubble {
  position: absolute;
  bottom: -20px;
  width: 10px;
  height: 10px;
  background: rgba(255, 255, 255, 0.5);
  border-radius: 50%;
  animation: rise linear infinite;
}

.bubble-1 { left: 20%; width: 8px; height: 8px; animation-duration: 6s; }
.bubble-2 { left: 45%; width: 12px; height: 12px; animation-duration: 8s; animation-delay: 1s; }
.bubble-3 { left: 70%; width: 6px; height: 6px; animation-duration: 5s; animation-delay: 2.5s; }
.bubble-4 { left: 85%; width: 10px; height: 10px; animation-duration: 7s; animation-delay: 0.5s; }

@keyframes rise {
  0% { bottom: -20px; opacity: 0.8; }
  90% { opacity: 0.6; }
  100% { bottom: 420px; opacity: 0; }
}

.seaweed {
  position: absolute;
  bottom: 0;
  width: 16px;
  height: 80px;
  background: #2e7d32;
  border-radius: 40px 40px 0 0;
  transform-origin: bottom center;
  animation: sway 3s ease-in-out infinite;
}

.seaweed-1 { left: 10%; height: 70px; animation-duration: 2.6s; }
.seaweed-2 { left: 50%; height: 90px; animation-duration: 3.4s; animation-delay: 0.5s; }
.seaweed-3 { left: 80%; height: 60px; animation-duration: 2.9s; animation-delay: 1s; }

@keyframes sway {
  0%, 100% { transform: rotate(-8deg); }
  50% { transform: rotate(8deg); }
}

#flash-overlay {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #ffffff;
  color: #111;
  font-size: 3rem;
  font-weight: bold;
  pointer-events: none;
  opacity: 0;
  z-index: 9999;
}

#flash-overlay.flash {
  animation: eye-flash 0.5s ease-out;
}

@keyframes eye-flash {
  0% { opacity: 0; }
  15% { opacity: 1; }
  100% { opacity: 0; }
}