:root {
  --bg: #050b17;
  --panel: rgba(12, 18, 31, 0.8);
  --panel-strong: rgba(18, 24, 38, 0.95);
  --panel-border: rgba(118, 170, 255, 0.35);
  --board-light: rgba(137, 165, 214, 0.8);
  --board-dark: rgba(39, 57, 85, 0.95);
  --board-selected: rgba(255, 194, 102, 0.9);
  --board-legal: rgba(78, 243, 174, 0.65);
  --board-capture: rgba(255, 120, 140, 0.8);
  --white-core: #dfeafc;
  --white-glow: #8ec5ff;
  --black-core: #1d2a3f;
  --black-glow: #77f0d4;
  --board-size: min(68vw, 720px);
  --shadow: 0 18px 40px rgba(0, 0, 0, 0.4);
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  min-height: 100%;
  background:
    radial-gradient(circle at top, rgba(61, 87, 159, 0.35), transparent 42%),
    linear-gradient(180deg, #040915 0%, #0a1120 100%);
  color: #edf6ff;
  font-family: "Noto Sans TC", sans-serif;
}

body {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 24px;
}

button, select {
  font: inherit;
}

.app-shell {
  width: min(1280px, 100%);
  padding: 22px 24px 18px;
  border: 1px solid rgba(123, 158, 255, 0.35);
  border-radius: 24px;
  background: rgba(5, 11, 23, 0.8);
  box-shadow: var(--shadow);
  backdrop-filter: blur(14px);
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 20px;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid rgba(162, 184, 255, 0.18);
}

.title-wrap {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.eyebrow {
  margin: 0;
  letter-spacing: 0.2em;
  font-size: 11px;
  color: #7ec9ff;
  font-family: "Orbitron", sans-serif;
}

h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 800;
  letter-spacing: 0.08em;
  font-family: "Orbitron", sans-serif;
}

.controls {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 12px;
}

.mode-toggle {
  display: inline-flex;
  padding: 6px;
  border-radius: 14px;
  border: 1px solid rgba(120, 174, 255, 0.4);
  background: rgba(17, 24, 37, 0.9);
}

.mode-button,
.new-game,
.side-picker select {
  border: none;
  border-radius: 10px;
  background: transparent;
  color: #dfeafc;
  cursor: pointer;
  transition: 180ms ease;
}

.mode-button {
  min-width: 120px;
  padding: 10px 16px;
  font-weight: 600;
  color: #bdd4ff;
}

.mode-button.active {
  background: linear-gradient(135deg, rgba(126, 188, 255, 0.35), rgba(90, 240, 211, 0.28));
  box-shadow: inset 0 0 0 1px rgba(143, 206, 255, 0.5);
  color: #ffffff;
}

.side-picker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  border: 1px solid rgba(120, 174, 255, 0.4);
  background: rgba(15, 21, 33, 0.9);
  border-radius: 12px;
  font-size: 0.95rem;
  color: #d8ebff;
}

.side-picker select {
  min-width: 88px;
  background: rgba(8, 13, 22, 0.9);
  border: 1px solid rgba(121, 170, 255, 0.35);
  color: #edf6ff;
  padding: 6px 10px;
}

.new-game {
  padding: 10px 18px;
  border: 1px solid rgba(120, 174, 255, 0.45);
  background: linear-gradient(135deg, rgba(103, 162, 255, 0.2), rgba(99, 240, 191, 0.2));
  font-weight: 700;
}

.game-layout {
  display: grid;
  grid-template-columns: minmax(420px, 1.2fr) minmax(260px, 0.8fr);
  gap: 24px;
}

.board-panel {
  display: flex;
  justify-content: center;
  align-items: center;
}

.board-frame {
  position: relative;
  width: min(100%, var(--board-size));
  aspect-ratio: 1;
  padding: 14px;
  border-radius: 26px;
  background: linear-gradient(135deg, rgba(28, 39, 58, 0.9), rgba(10, 19, 35, 0.95));
  border: 1px solid rgba(130, 175, 255, 0.35);
  box-shadow: inset 0 0 20px rgba(99, 157, 255, 0.18);
}

.board {
  position: relative;
  display: grid;
  grid-template-columns: repeat(8, minmax(0, 1fr));
  width: 100%;
  height: 100%;
  overflow: hidden;
  border-radius: 18px;
  border: 2px solid rgba(118, 171, 255, 0.25);
  background: rgba(7, 14, 22, 0.8);
}

.square {
  position: relative;
  display: grid;
  place-items: center;
  user-select: none;
}

.square.light {
  background: linear-gradient(135deg, rgba(159, 178, 214, 0.88), rgba(101, 128, 176, 0.82));
}

.square.dark {
  background: linear-gradient(135deg, rgba(38, 56, 82, 0.9), rgba(17, 28, 40, 0.95));
}

.square.selected {
  box-shadow: inset 0 0 0 4px rgba(255, 203, 106, 0.9);
}

.square.legal::after,
.square.capture::after {
  content: "";
  position: absolute;
  inset: 50% auto auto 50%;
  width: 22%;
  height: 22%;
  border-radius: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
}

.square.legal::after {
  background: rgba(98, 255, 183, 0.7);
  box-shadow: 0 0 18px rgba(70, 235, 178, 0.8);
}

.square.capture::after {
  background: rgba(255, 98, 123, 0.7);
  box-shadow: 0 0 20px rgba(255, 120, 140, 0.9);
}

.piece {
  position: relative;
  display: grid;
  place-items: center;
  width: 74%;
  height: 74%;
  margin: auto;
  border-radius: 24% 24% 32% 32%;
  border: 2px solid rgba(255, 255, 255, 0.26);
  background: linear-gradient(135deg, rgba(255, 255, 255, 0.1), rgba(7, 15, 24, 0.3));
  box-shadow: inset 0 0 12px rgba(255, 255, 255, 0.12), 0 0 22px rgba(122, 176, 255, 0.18);
  transition: transform 220ms ease, box-shadow 220ms ease;
}

.piece:hover {
  transform: translateY(-2px) scale(1.02);
}

.piece::before {
  content: "";
  position: absolute;
  inset: 12% 18% 18% 18%;
  border-radius: 50% 50% 44% 44%;
  background: radial-gradient(circle at 30% 25%, rgba(255, 255, 255, 0.85), rgba(255, 255, 255, 0.08) 28%, rgba(0, 0, 0, 0) 55%);
  opacity: 0.95;
}

.piece::after {
  content: attr(data-char);
  position: relative;
  z-index: 1;
  display: block;
  font-size: clamp(1.5rem, 2vw, 2.3rem);
  font-weight: 800;
  letter-spacing: 0.06em;
  font-family: "Orbitron", sans-serif;
  text-shadow: 0 0 10px currentColor;
}

.piece.white {
  color: var(--white-core);
  background: linear-gradient(135deg, rgba(188, 218, 255, 0.9), rgba(17, 33, 67, 0.75));
  box-shadow: inset 0 0 8px rgba(255, 255, 255, 0.35), 0 0 24px rgba(142, 197, 255, 0.45);
}

.piece.black {
  color: var(--black-core);
  background: linear-gradient(135deg, rgba(37, 52, 76, 0.95), rgba(9, 20, 32, 0.9));
  box-shadow: inset 0 0 8px rgba(122, 255, 216, 0.3), 0 0 24px rgba(119, 240, 212, 0.32);
}

.sidebar {
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 18px;
  padding: 18px 18px 16px;
  box-shadow: inset 0 0 0 1px rgba(142, 181, 255, 0.06);
}

.panel h2 {
  margin: 0 0 12px;
  font-size: 1rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #b8d9ff;
  font-family: "Orbitron", sans-serif;
}

.status-text {
  margin: 0;
  font-size: 1.05rem;
  color: #ecf7ff;
  font-weight: 700;
}

.move-log {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
  max-height: 280px;
  overflow: auto;
}

.move-log li {
  padding: 8px 10px;
  border-radius: 10px;
  background: rgba(20, 31, 47, 0.8);
  border: 1px solid rgba(125, 171, 255, 0.2);
  color: #dfeeff;
  font-size: 0.96rem;
}

.impact-overlay {
  position: relative;
  min-height: 160px;
  padding: 14px;
  border-radius: 16px;
  border: 1px solid rgba(130, 183, 255, 0.24);
  background: linear-gradient(180deg, rgba(16, 22, 35, 0.8), rgba(10, 18, 29, 0.95));
  overflow: hidden;
  display: grid;
  place-items: center;
}

.impact-overlay::before {
  content: "";
  position: absolute;
  inset: 18% 12% 18% 12%;
  border-radius: 14px;
  border: 1px solid rgba(126, 192, 255, 0.2);
  background: radial-gradient(circle at center, rgba(124, 206, 255, 0.14), transparent 60%);
}

.impact-card {
  position: relative;
  z-index: 1;
  display: grid;
  gap: 8px;
  text-align: center;
  opacity: 0;
  transform: translateY(12px) scale(0.94);
}

.impact-overlay.show .impact-card {
  animation: impactIn 900ms ease forwards;
}

.game-over-banner {
  position: absolute;
  inset: 50% auto auto 50%;
  transform: translate(-50%, -50%);
  padding: 12px 22px;
  border-radius: 999px;
  background: rgba(12, 22, 35, 0.9);
  border: 1px solid rgba(123, 181, 255, 0.5);
  box-shadow: 0 0 24px rgba(78, 154, 255, 0.32);
  color: #f2fbff;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.impact-title {
  font-size: 1.1rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  color: #f7fbff;
}

.impact-method {
  font-size: 0.85rem;
  color: #8dd7ff;
  letter-spacing: 0.06em;
}

.impact-victim {
  margin-top: 2px;
  font-size: 1.8rem;
}

@keyframes impactIn {
  0% {
    opacity: 0;
    transform: translateY(16px) scale(0.9);
  }
  20% {
    opacity: 1;
    transform: translateY(0) scale(1.02);
  }
  65% {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
  100% {
    opacity: 0;
    transform: translateY(-16px) scale(1.02);
  }
}

@media (max-width: 980px) {
  .game-layout {
    grid-template-columns: 1fr;
  }

  .topbar {
    flex-direction: column;
    align-items: stretch;
  }

  .controls {
    justify-content: flex-start;
  }
}

@media (max-width: 540px) {
  body {
    padding: 12px;
  }

  .app-shell {
    padding: 16px 12px 14px;
  }

  .mode-button {
    flex: 1 1 42%;
  }

  .controls {
    flex-direction: column;
    align-items: stretch;
  }

  .side-picker {
    justify-content: space-between;
  }
}