:root {
  /* Dark Mode (Default) */
  --water-bg: #001f24;
  --water-color: #004d56;
  --text-color: rgba(255, 255, 255, 0.9);
  --btn-bg: rgba(255, 255, 255, 0.1);
  --btn-hover: rgba(255, 255, 255, 0.2);
}

[data-theme="light"] {
  --water-bg: #e0f7fa;
  --water-color: #81d4fa;
  --text-color: rgba(0, 77, 64, 0.9);
  --btn-bg: rgba(0, 0, 0, 0.05);
  --btn-hover: rgba(0, 0, 0, 0.1);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body, html {
  width: 100%;
  height: 100%;
  overflow: hidden;
  background-color: var(--water-bg);
  transition: background-color 0.5s ease;
  font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, 'Helvetica Neue', 'Segoe UI', 'Apple SD Gothic Neo', 'Noto Sans KR', 'Malgun Gothic', sans-serif;
}

#river-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 1;
}

#theme-toggle {
  position: fixed;
  top: 2rem;
  right: 2rem;
  z-index: 100;
  width: 3rem;
  height: 3rem;
  border-radius: 50%;
  border: none;
  background-color: var(--btn-bg);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

#theme-toggle:hover {
  background-color: var(--btn-hover);
  transform: scale(1.1);
}

.mode-icon {
  position: relative;
  width: 1.2rem;
  height: 1.2rem;
  border-radius: 50%;
  background-color: var(--text-color);
  transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Sun/Moon effect using box-shadow for light mode */
[data-theme="light"] .mode-icon {
  background-color: transparent;
  box-shadow: inset -4px -4px 0 0 var(--text-color);
  transform: rotate(-20deg);
}

/* Subtle grain overlay */
body::after {
  content: "";
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3%3Ffilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
  opacity: 0.05;
  pointer-events: none;
  z-index: 2;
}