:root {
  color-scheme: dark;
  --page-bg: radial-gradient(circle at 20% 20%, #1f2945, #080b16 70%);
  --text-primary: #f8fafc;
  --text-secondary: rgba(226, 232, 240, 0.72);
  --accent: #38bdf8;
  --accent-strong: #0ea5e9;
  --panel-bg: rgba(15, 23, 42, 0.6);
  --panel-border: rgba(148, 163, 184, 0.18);
  --grid-blue-1: #1e3a8a;
  --grid-blue-2: #0f172a;
  --disc-player: #fbbf24;
  --disc-ai: #38bdf8;
  --disc-preview: rgba(251, 191, 36, 0.32);
  --ease-bounce: cubic-bezier(0.22, 1.15, 0.38, 1.02);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Manrope", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--page-bg);
  color: var(--text-primary);
  display: flex;
  align-items: stretch;
  justify-content: center;
}

.page {
  width: min(960px, 92vw);
  margin: clamp(48px, 8vh, 84px) auto;
  display: flex;
  flex-direction: column;
  gap: clamp(32px, 7vh, 48px);
}

.intro {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 24px;
}

.intro__text {
  max-width: 620px;
}

.intro__title {
  font-size: clamp(36px, 6vw, 56px);
  letter-spacing: -0.04em;
  margin: 0 0 12px;
}

.intro__subtitle {
  margin: 0;
  font-size: clamp(16px, 2.4vw, 18px);
  line-height: 1.55;
  color: var(--text-secondary);
}

.ghost-button {
  appearance: none;
  border: 1px solid rgba(148, 163, 184, 0.28);
  background: transparent;
  color: var(--text-primary);
  font: inherit;
  padding: 11px 18px;
  border-radius: 999px;
  cursor: pointer;
  transition: border-color 0.25s ease, background-color 0.25s ease, transform 0.2s ease;
}

.ghost-button:hover {
  border-color: rgba(148, 163, 184, 0.48);
  background: rgba(148, 163, 184, 0.12);
  transform: translateY(-1px);
}

.panel {
  padding: clamp(20px, 3vh, 28px);
  border-radius: 24px;
  border: 1px solid var(--panel-border);
  background: linear-gradient(135deg, rgba(15, 23, 42, 0.65), rgba(15, 23, 42, 0.35));
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 24px;
  backdrop-filter: blur(16px);
}

.panel__section {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.label {
  text-transform: uppercase;
  font-size: 11px;
  letter-spacing: 0.28em;
  color: rgba(226, 232, 240, 0.48);
}

.difficulty {
  display: inline-flex;
  padding: 6px;
  border-radius: 999px;
  background: rgba(15, 23, 42, 0.65);
  border: 1px solid rgba(148, 163, 184, 0.18);
  gap: 6px;
}

.difficulty__option {
  appearance: none;
  border: none;
  background: transparent;
  padding: 10px 16px;
  border-radius: 999px;
  font: inherit;
  color: rgba(226, 232, 240, 0.7);
  cursor: pointer;
  transition: color 0.2s ease, background-color 0.2s ease, transform 0.2s ease;
}

.difficulty__option:hover {
  color: var(--text-primary);
}

.difficulty__option.is-active {
  background: radial-gradient(circle at 30% 30%, rgba(56, 189, 248, 0.45), rgba(14, 165, 233, 0.25));
  color: var(--text-primary);
  box-shadow: 0 10px 22px rgba(14, 165, 233, 0.25);
}

.status {
  margin: 0;
  font-size: clamp(16px, 2.5vw, 18px);
  color: var(--text-secondary);
}

.board-area {
  display: flex;
  justify-content: center;
}

.board-shadow {
  position: relative;
  padding: clamp(12px, 2vw, 18px);
  border-radius: 36px;
  background: linear-gradient(145deg, rgba(30, 64, 175, 0.26), rgba(30, 64, 175, 0.06));
  box-shadow:
    0 24px 48px rgba(8, 10, 22, 0.65),
    inset 0 1px 0 rgba(148, 163, 184, 0.12);
}

.board {
  position: relative;
  --cell-size: clamp(70px, 10vw, 92px);
  --disc-gap: clamp(12px, 1.8vw, 18px);
  --board-padding: clamp(18px, 2.2vw, 28px);
  width: calc(var(--cell-size) * 7 + var(--board-padding) * 2);
  height: calc(var(--cell-size) * 6 + var(--board-padding) * 2);
  background: linear-gradient(145deg, rgba(14, 165, 233, 0.48), rgba(14, 116, 233, 0.16));
  border-radius: calc(var(--cell-size) * 0.32);
  box-shadow:
    inset 0 20px 36px rgba(8, 10, 22, 0.35),
    inset 0 -18px 24px rgba(30, 64, 175, 0.45);
  cursor: pointer;
}

.slot-grid,
.disc-layer {
  position: absolute;
  inset: var(--board-padding);
}

.slot-grid {
  display: grid;
  grid-template-columns: repeat(7, var(--cell-size));
  grid-template-rows: repeat(6, var(--cell-size));
  gap: 0;
}

.slot {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
}

.slot::before {
  content: "";
  width: calc(var(--cell-size) - var(--disc-gap));
  height: calc(var(--cell-size) - var(--disc-gap));
  border-radius: 50%;
  background: radial-gradient(circle at 35% 30%, rgba(255, 255, 255, 0.18), rgba(15, 23, 42, 0.85));
  box-shadow:
    inset 0 8px 16px rgba(8, 10, 22, 0.55),
    inset 0 -6px 12px rgba(30, 64, 175, 0.25);
}

.disc-layer {
  pointer-events: none;
  overflow: visible;
}

.disc {
  position: absolute;
  width: calc(var(--cell-size) - var(--disc-gap));
  height: calc(var(--cell-size) - var(--disc-gap));
  border-radius: 50%;
  left: calc(var(--col) * var(--cell-size) + var(--disc-gap) * 0.5);
  top: calc(-1 * var(--cell-size));
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(255, 255, 255, 0.16);
  box-shadow:
    0 10px 24px rgba(8, 10, 22, 0.4),
    inset 0 8px 16px rgba(255, 255, 255, 0.2),
    inset 0 -8px 16px rgba(8, 10, 22, 0.3);
  transition: top 0.45s var(--ease-bounce),
    filter 0.35s ease,
    opacity 0.3s ease;
  pointer-events: none;
}

.disc.dropping {
  top: calc(var(--row) * var(--cell-size) + var(--disc-gap) * 0.5);
}

.disc.player {
  background: radial-gradient(circle at 30% 25%, rgba(255, 221, 120, 0.95), rgba(251, 191, 36, 0.85));
  box-shadow:
    0 14px 32px rgba(251, 191, 36, 0.35),
    inset 0 10px 18px rgba(255, 255, 255, 0.35),
    inset 0 -8px 16px rgba(180, 83, 9, 0.45);
}

.disc.ai {
  background: radial-gradient(circle at 30% 25%, rgba(125, 211, 252, 0.95), rgba(14, 165, 233, 0.85));
  box-shadow:
    0 14px 32px rgba(14, 165, 233, 0.35),
    inset 0 10px 18px rgba(255, 255, 255, 0.25),
    inset 0 -8px 16px rgba(30, 64, 175, 0.55);
}

.disc.preview {
  opacity: 0;
  top: calc(-1.4 * var(--cell-size));
  background: radial-gradient(circle at 30% 25%, rgba(251, 191, 36, 0.55), rgba(251, 191, 36, 0.2));
  box-shadow: none;
  transition: left 0.2s ease, opacity 0.25s ease, top 0.25s ease, transform 0.25s ease;
}

.disc.preview.is-visible {
  opacity: 1;
}

.disc.preview.bounce {
  animation: preview-bounce 0.25s ease;
}

.disc.faded {
  filter: saturate(0.35) brightness(0.85);
}

.disc.winning {
  filter: none;
  box-shadow:
    0 16px 36px rgba(248, 250, 252, 0.32),
    inset 0 12px 20px rgba(255, 255, 255, 0.5),
    inset 0 -10px 18px rgba(14, 116, 233, 0.35);
  z-index: 2;
}

@keyframes preview-bounce {
  0% {
    transform: translateY(0);
  }
  55% {
    transform: translateY(calc(-0.2 * var(--cell-size)));
  }
  100% {
    transform: translateY(0);
  }
}

.tips {
  color: rgba(226, 232, 240, 0.52);
  font-size: 14px;
  line-height: 1.6;
  text-align: center;
  margin: 0 auto;
}

@media (max-width: 780px) {
  .intro {
    flex-direction: column;
    align-items: stretch;
  }

  .ghost-button {
    align-self: flex-start;
  }
}

@media (max-width: 640px) {
  .page {
    width: min(480px, 92vw);
    gap: 28px;
  }

  .panel {
    grid-template-columns: 1fr;
  }

  .board-shadow {
    padding: 10px;
    border-radius: 28px;
  }
}

@media (max-height: 720px) {
  .page {
    margin: clamp(24px, 5vh, 48px) auto;
  }

  .board {
    --cell-size: clamp(60px, 9vh, 82px);
  }
}