body {
    min-height: 100vh;
    background-color: #0b1120;
    background-image: radial-gradient(ellipse at 30% 20%, rgba(30, 58, 138, 0.12) 0%, transparent 60%),
                      radial-gradient(ellipse at 70% 80%, rgba(88, 28, 135, 0.10) 0%, transparent 60%);
    color: #e2e8f0;
    font-family: "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
    margin: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
}

header { text-align: center; padding: 40px 16px 16px; }
h1 { font-size: 1.6rem; font-weight: 700; margin: 0; }

main {
    width: 100%;
    max-width: 760px;
    padding: 0 16px 60px;
}

.game-layout {
    display: flex;
    gap: 18px;
    justify-content: center;
    align-items: flex-start;
    flex-wrap: wrap;
}

/* ---- side panel ---- */
.side-panel {
    display: flex;
    flex-direction: column;
    gap: 14px;
    min-width: 140px;
    padding: 16px;
    background: rgba(30, 41, 59, 0.5);
    border: 1px solid rgba(148, 163, 184, 0.1);
    border-radius: 14px;
    backdrop-filter: blur(10px);
}
.panel-section { text-align: center; }
.panel-label {
    font-size: 0.7rem;
    color: #64748b;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-bottom: 4px;
}
.panel-value {
    font-size: 1.4rem;
    font-weight: 700;
    font-variant-numeric: tabular-nums;
    color: #a5b4fc;
}
#nextCanvas, #holdCanvas {
    background: rgba(15, 23, 42, 0.7);
    border-radius: 6px;
    margin: 0 auto;
    display: block;
}

.controls { text-align: left; margin-top: 4px; }
.controls .panel-label { margin-bottom: 6px; }
.key-row {
    font-size: 0.78rem;
    color: #94a3b8;
    margin: 4px 0;
    display: flex;
    align-items: center;
    gap: 4px;
    flex-wrap: wrap;
}
kbd {
    display: inline-block;
    padding: 1px 6px;
    font-size: 0.72rem;
    font-family: monospace;
    background: rgba(148, 163, 184, 0.1);
    border: 1px solid rgba(148, 163, 184, 0.25);
    border-radius: 4px;
    color: #cbd5e1;
}

/* ---- board ---- */
.board-wrapper {
    position: relative;
}
#board {
    display: block;
    background: #0a1124;
    border: 2px solid rgba(96, 165, 250, 0.25);
    border-radius: 8px;
}

.overlay {
    position: absolute;
    inset: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 16px;
    background: rgba(11, 17, 32, 0.85);
    border-radius: 8px;
    transition: opacity 0.25s;
}
.overlay.hidden { opacity: 0; pointer-events: none; }
.overlay-text {
    font-size: 1.3rem;
    font-weight: 700;
    color: #a5b4fc;
    text-align: center;
    padding: 0 16px;
}
.start-btn {
    padding: 10px 28px;
    font-size: 0.95rem;
    font-weight: 700;
    border: 1px solid rgba(129, 140, 248, 0.4);
    border-radius: 10px;
    background: linear-gradient(135deg, #60a5fa, #a78bfa);
    color: #0b1120;
    cursor: pointer;
    transition: transform 0.15s, box-shadow 0.2s;
}
.start-btn:hover { transform: translateY(-2px); box-shadow: 0 6px 20px rgba(96, 165, 250, 0.4); }

@media (max-width: 720px) {
    header { padding-top: 24px; }
    .game-layout { flex-direction: column; align-items: center; }
    .side-panel { min-width: 280px; flex-direction: row; flex-wrap: wrap; justify-content: center; gap: 18px; }
    .panel-section { min-width: 70px; }
}