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

:root {
    --bg: #141518;
    --panel: #23262c;
    --line: #3c424c;
    --text: #fbf1e4;
    --muted: #a3adbb;
    --accent: #6fb1ff;
    --light: #eadfc8;
    --dark: #7d8a99;
}

html, body { height: 100%; overscroll-behavior: none; }

body {
    position: fixed; inset: 0; overflow: hidden;
    color: var(--text);
    font-family: 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'Segoe UI', sans-serif;
    background:
        radial-gradient(circle at 50% 0%, rgba(111, 177, 255, 0.12), transparent 55%),
        linear-gradient(180deg, #0d0e11, #191c22);
    user-select: none; -webkit-user-select: none;
    -webkit-tap-highlight-color: transparent;
    touch-action: none;
}

.shell {
    display: flex; flex-direction: column;
    height: 100%; min-height: 100dvh;
    max-width: 520px; margin: 0 auto;
    padding:
        max(6px, env(safe-area-inset-top))
        max(8px, env(safe-area-inset-right))
        max(8px, env(safe-area-inset-bottom))
        max(8px, env(safe-area-inset-left));
}

.toolbar { display: flex; align-items: center; gap: 6px; flex: 0 0 auto; height: 38px; }
.toolbar-spacer { flex: 1; }

.icon-btn {
    display: inline-flex; align-items: center; justify-content: center;
    min-width: 34px; height: 31px; padding: 0 10px;
    border: 1px solid var(--line); border-radius: 9px;
    background: var(--panel); color: var(--text);
    font-family: inherit; font-size: 0.88rem; line-height: 1;
    text-decoration: none; cursor: pointer;
    transition: transform 0.12s ease, border-color 0.12s ease;
}

.icon-btn-text { font-size: 0.76rem; font-weight: 600; }
.icon-btn:active { transform: scale(0.94); border-color: var(--accent); }

.hud { display: flex; gap: 5px; flex: 0 0 auto; margin: 5px 0; }

.hud span {
    flex: 1; display: flex; flex-direction: column; align-items: center;
    padding: 4px 2px; border-radius: 9px; background: rgba(255, 255, 255, 0.05);
}

.hud b { font-size: 0.86rem; font-variant-numeric: tabular-nums; }
.hud b.is-white { color: #f2f5f9; }
.hud b.is-black { color: #93a4b8; }
.hud i { font-style: normal; font-size: 0.56rem; letter-spacing: 0.08em; color: var(--muted); }

/* The captured pieces of each side, above and below the board. Seeing what has
   come off tells you more about the position at a glance than any number. */
.taken {
    flex: 0 0 auto; min-height: 20px; align-self: stretch;
    display: flex; align-items: center; gap: 2px; flex-wrap: wrap;
    padding: 0 2px; font-size: 0.8rem; line-height: 1;
}
.taken u { font-style: normal; text-decoration: none; opacity: 0.85; }
.taken u.white { color: #f0f3f7; }
.taken u.black { color: #8fa0b4; }

.board-area { flex: 1 1 auto; min-height: 0; display: flex; align-items: center; justify-content: center; }

/* The board with its two rows of captured pieces, kept together and centred as
   one block. The board's shape is fixed, so on a tall screen the spare height
   is above and below this stack rather than between its parts. */
.board-stack { display: flex; flex-direction: column; align-items: center; gap: 2px; min-height: 0; }

#board {
    display: block;
    border-radius: 8px;
    box-shadow: 0 14px 36px rgba(0, 0, 0, 0.5);
    touch-action: none;
}

.tools { display: flex; gap: 6px; flex: 0 0 auto; margin-top: 8px; }

.tool {
    flex: 1; min-height: 52px;
    display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 1px;
    border: 1px solid var(--line); border-radius: 12px;
    background: var(--panel); color: var(--text);
    font-family: inherit; cursor: pointer; transition: transform 0.1s ease;
}

.tool i { font-style: normal; font-size: 1.05rem; line-height: 1; }
.tool span { font-size: 0.6rem; color: var(--muted); }
.tool:active { transform: scale(0.96); }
.tool:disabled { opacity: 0.4; }

.hint-text { margin-top: 5px; text-align: center; font-size: 0.66rem; color: var(--muted); min-height: 1.2em; }
.hint-text.is-warn { color: #ffb08e; font-weight: 700; }

.overlay {
    position: absolute; inset: 0; display: none;
    align-items: center; justify-content: center; padding: 18px;
    background: rgba(9, 6, 4, 0.9);
    backdrop-filter: blur(5px); -webkit-backdrop-filter: blur(5px);
    z-index: 50;
}

.overlay.is-open { display: flex; }

.panel {
    width: 100%; max-width: 340px; max-height: 100%; overflow-y: auto;
    display: flex; flex-direction: column; gap: 10px;
    padding: 22px 18px;
    border: 1px solid var(--line); border-radius: 20px;
    background: linear-gradient(180deg, #2b3038, #171a1f);
    text-align: center; animation: pop 0.22s ease;
}

@keyframes pop { from { opacity: 0; transform: translateY(12px) scale(0.97); } to { opacity: 1; transform: none; } }

.title {
    font-size: clamp(1.9rem, 9vw, 2.5rem); font-weight: 800; letter-spacing: 0.18em;
    background: linear-gradient(135deg, #bcdcff, var(--accent) 60%, #4f7fd6);
    -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent;
}

.panel-title { font-size: 1.5rem; font-weight: 800; letter-spacing: 0.08em; color: var(--accent); }
.subtitle { color: var(--muted); font-size: 0.85rem; line-height: 1.7; }

.modes { display: flex; flex-direction: column; gap: 8px; margin-top: 4px; }

.mode {
    display: flex; align-items: center; justify-content: space-between;
    padding: 13px 16px;
    border: 1px solid var(--line); border-radius: 13px;
    background: rgba(255, 255, 255, 0.05); color: var(--text);
    font-family: inherit; font-size: 0.95rem; font-weight: 700; cursor: pointer;
    transition: transform 0.12s ease, border-color 0.12s ease;
}

.mode small { font-size: 0.68rem; font-weight: 500; color: var(--muted); }
.mode:active { transform: scale(0.98); border-color: var(--accent); }

/* What each piece does. The characters are the game itself, so they are never
   translated away -- the explanation beside them is. */
.legend { display: flex; flex-direction: column; gap: 5px; margin-top: 6px; text-align: left; }
.legend h3 { font-size: 0.7rem; letter-spacing: 0.1em; color: var(--muted); font-weight: 600; }
.legend-row { display: flex; align-items: baseline; gap: 8px; font-size: 0.72rem; color: var(--muted); }
.legend-row b {
    flex: 0 0 auto; width: 1.7em; height: 1.7em;
    font-family: "Segoe UI Symbol", "Apple Symbols", serif;
    display: inline-flex; align-items: center; justify-content: center;
    border-radius: 50%; border: 1px solid #8a6437;
    background: var(--light); color: #23262c;
    font-size: 0.82rem; font-weight: 800;
}

.btn {
    min-height: 46px; padding: 12px 20px;
    border: 1px solid var(--line); border-radius: 13px;
    background: rgba(255, 255, 255, 0.05); color: var(--text);
    font-family: inherit; font-size: 0.92rem; font-weight: 700;
    text-decoration: none; display: flex; align-items: center; justify-content: center;
    cursor: pointer;
}

.btn:active { transform: scale(0.97); }
.btn-primary { border-color: transparent; background: linear-gradient(135deg, #a9d0ff, #4f8fe0); color: #06101f; }

.stat-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 7px; }
.stat { padding: 9px 6px; border-radius: 11px; background: rgba(255, 255, 255, 0.06); }
.stat b { display: block; font-size: 1.1rem; font-variant-numeric: tabular-nums; }
.stat span { font-size: 0.62rem; color: var(--muted); }

@media (max-height: 700px) {
    .hud { margin: 3px 0; }
    .tool { min-height: 44px; }
    .hint-text { display: none; }
    .taken { min-height: 18px; font-size: 0.72rem; }
}

@media (prefers-reduced-motion: reduce) { .panel { animation: none; } }

/* Choosing what a pawn becomes. It appears only in the moment between the pawn
   reaching the far rank and the move being made, so it is a small row of
   pieces rather than a full screen. */
.promo-row { display: flex; gap: 8px; justify-content: center; margin-top: 4px; }

.promo-btn {
    width: 56px; height: 56px;
    display: flex; align-items: center; justify-content: center;
    border: 1px solid var(--line); border-radius: 13px;
    background: var(--light); color: #1b1e24;
    font-family: "Segoe UI Symbol", "Apple Symbols", serif;
    font-size: 2rem; line-height: 1; cursor: pointer;
}
.promo-btn:active { transform: scale(0.95); border-color: var(--accent); }