:root {
    --ff-gold: #d4a843;
    --ff-gold-dark: #8b6914;
    --ff-blue: #1a3a5c;
    --ff-blue-dark: #0a1628;
    --ff-blue-light: #2a5a8c;
    --ff-red: #c0392b;
    --ff-red-light: #e74c3c;
    --ff-crystal: #4fc3f7;
    --ff-purple: #7c4dff;
    --ff-text: #e8d5a3;
    --ff-text-dim: #8a7a5a;
    --ff-bg-dark: #0a0e1a;
    --ff-bg-panel: rgba(10, 14, 26, 0.85);
    --ff-border: rgba(212, 168, 67, 0.3);
    --ff-glow: rgba(79, 195, 247, 0.3);
}

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

body {
    background: var(--ff-bg-dark);
    color: var(--ff-text);
    font-family: 'Cinzel', 'Noto Serif SC', serif;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow-x: hidden;
}

#particles-bg {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%; z-index: 0;
    background:
        radial-gradient(ellipse at 20% 50%, rgba(26,58,92,0.4) 0%, transparent 50%),
        radial-gradient(ellipse at 80% 20%, rgba(124,77,255,0.15) 0%, transparent 50%),
        radial-gradient(ellipse at 50% 80%, rgba(79,195,247,0.1) 0%, transparent 50%);
    animation: bgPulse 8s ease-in-out infinite alternate;
}

@keyframes bgPulse { 0% { opacity: 0.8; } 100% { opacity: 1; } }

#particles-bg::before, #particles-bg::after {
    content: ''; position: absolute; width: 2px; height: 2px;
    background: var(--ff-crystal); border-radius: 50%;
    box-shadow:
        100px 50px 0 var(--ff-crystal), 300px 150px 0 var(--ff-purple),
        500px 80px 0 var(--ff-gold), 200px 300px 0 var(--ff-crystal),
        400px 200px 0 var(--ff-purple), 600px 350px 0 var(--ff-crystal),
        150px 400px 0 var(--ff-gold), 700px 100px 0 var(--ff-crystal),
        50px 250px 0 var(--ff-purple), 350px 450px 0 var(--ff-gold),
        800px 300px 0 var(--ff-crystal), 250px 500px 0 var(--ff-purple),
        900px 150px 0 var(--ff-gold), 450px 350px 0 var(--ff-crystal),
        650px 450px 0 var(--ff-purple), 100px 550px 0 var(--ff-crystal);
    animation: floatParticles 15s linear infinite; opacity: 0.4;
}

#particles-bg::after { animation-delay: -7s; opacity: 0.3; }

@keyframes floatParticles {
    0% { transform: translateY(0) translateX(0); }
    25% { transform: translateY(-30px) translateX(10px); }
    50% { transform: translateY(-10px) translateX(-15px); }
    75% { transform: translateY(-40px) translateX(5px); }
    100% { transform: translateY(0) translateX(0); }
}

.hidden { display: none !important; }

#menuParticles {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    z-index: 0; pointer-events: none;
}

.main-menu {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    z-index: 10; display: flex; align-items: center; justify-content: center;
    background: transparent;
}

.menu-content {
    text-align: center; z-index: 11; position: relative;
    animation: menuFadeIn 1s ease-out;
}

@keyframes menuFadeIn {
    0% { opacity: 0; transform: translateY(30px); }
    100% { opacity: 1; transform: translateY(0); }
}

.logo-container {
    position: relative; margin-bottom: 50px;
}

.logo-glow {
    position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%);
    width: 400px; height: 400px;
    background: radial-gradient(circle, rgba(212,168,67,0.08) 0%, rgba(79,195,247,0.04) 40%, transparent 70%);
    border-radius: 50%; animation: logoGlowPulse 4s ease-in-out infinite alternate;
    pointer-events: none;
}

@keyframes logoGlowPulse {
    0% { opacity: 0.5; transform: translate(-50%, -50%) scale(0.95); }
    100% { opacity: 1; transform: translate(-50%, -50%) scale(1.05); }
}

.logo-crystals {
    display: flex; justify-content: center; gap: 30px; margin-bottom: 25px;
}

.lcrystal {
    font-size: 28px; display: inline-block;
    animation: crystalBob 3s ease-in-out infinite;
    filter: drop-shadow(0 0 10px rgba(79,195,247,0.6));
}

.left-c { animation-delay: 0s; }
.center-c { font-size: 36px; animation-delay: 0.5s; }
.right-c { animation-delay: 1s; }

@keyframes crystalBob {
    0%, 100% { transform: translateY(0) rotate(0deg); }
    50% { transform: translateY(-8px) rotate(5deg); }
}

.logo-emblem {
    width: 100px; height: 100px; margin: 0 auto 20px; position: relative;
    display: flex; align-items: center; justify-content: center;
}

.emblem-ring {
    position: absolute; border-radius: 50%;
    border: 1px solid var(--ff-gold);
}

.outer-ring {
    width: 100px; height: 100px; top: 0; left: 0;
    border-color: rgba(212,168,67,0.4);
    animation: emblemSpin 20s linear infinite;
}

.inner-ring {
    width: 80px; height: 80px; top: 10px; left: 10px;
    border-color: rgba(79,195,247,0.3);
    animation: emblemSpin 15s linear infinite reverse;
}

@keyframes emblemSpin { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); } }

.emblem-core {
    width: 60px; height: 60px; border-radius: 50%; z-index: 2;
    background: linear-gradient(135deg, #1a1a2e, #0f0f1e);
    border: 2px solid var(--ff-gold);
    display: flex; align-items: center; justify-content: center;
    box-shadow: 0 0 20px rgba(212,168,67,0.3), inset 0 0 15px rgba(0,0,0,0.5);
}

.emblem-char {
    font-family: 'Noto Serif SC', serif; font-size: 28px; font-weight: 900;
    background: linear-gradient(180deg, #ffd700, #d4a843);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 6px rgba(212,168,67,0.5));
}

.logo-title {
    display: flex; flex-direction: column; align-items: center; gap: 2px;
}

.logo-line-1 {
    font-family: 'Cinzel', serif; font-size: 38px; font-weight: 900;
    background: linear-gradient(180deg, #f0d878, #d4a843, #8b6914);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 15px rgba(212,168,67,0.4));
    letter-spacing: 10px;
}

.logo-line-2 {
    font-family: 'Noto Serif SC', serif; font-size: 52px; font-weight: 900;
    background: linear-gradient(180deg, #ffd700, #d4a843);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 20px rgba(212,168,67,0.5));
    letter-spacing: 20px; margin: 5px 0;
}

.logo-line-3 {
    font-family: 'Cinzel', serif; font-size: 12px; color: var(--ff-text-dim);
    letter-spacing: 8px;
}

.logo-deco-line {
    display: flex; align-items: center; justify-content: center; gap: 10px;
    margin-top: 15px;
}

.deco-diamond { color: var(--ff-gold); font-size: 10px; }
.deco-star { color: var(--ff-crystal); font-size: 14px; }
.deco-line {
    width: 80px; height: 1px;
    background: linear-gradient(90deg, transparent, var(--ff-gold), transparent);
}

.menu-buttons {
    display: flex; flex-direction: column; gap: 16px; align-items: center;
    margin-bottom: 40px;
}

.menu-btn {
    position: relative; width: 360px; padding: 18px 30px;
    background: transparent; border: none; cursor: pointer;
    display: flex; align-items: center; gap: 16px;
    transition: transform 0.3s ease;
    overflow: hidden;
}

.menu-btn:hover { transform: scale(1.03); }
.menu-btn:active { transform: scale(0.98); }

.menu-btn-bg {
    position: absolute; top: 0; left: 0; width: 100%; height: 100%;
    background: linear-gradient(90deg, transparent 0%, rgba(10,14,26,0.9) 10%, rgba(10,14,26,0.95) 90%, transparent 100%);
    border-top: 1px solid var(--ff-border);
    border-bottom: 1px solid var(--ff-border);
    transition: all 0.3s ease;
}

.menu-btn:hover .menu-btn-bg {
    background: linear-gradient(90deg, transparent 0%, rgba(26,58,92,0.8) 10%, rgba(26,58,92,0.9) 90%, transparent 100%);
    border-color: var(--ff-gold);
    box-shadow: 0 0 20px rgba(212,168,67,0.15);
}

.primary-btn .menu-btn-bg { border-left: 3px solid var(--ff-gold); }
.secondary-btn .menu-btn-bg { border-left: 3px solid var(--ff-crystal); }
.exit-btn .menu-btn-bg { border-left: 3px solid #666; }
.exit-btn:hover .menu-btn-bg { border-color: #888; box-shadow: 0 0 10px rgba(136,136,136,0.1); }
.exit-btn .menu-btn-title { color: var(--ff-text-dim); }

.menu-btn-icon { font-size: 28px; z-index: 1; position: relative; }

.menu-btn-content {
    display: flex; flex-direction: column; align-items: flex-start; z-index: 1; position: relative;
}

.menu-btn-title {
    font-family: 'Noto Serif SC', serif; font-size: 20px; font-weight: 700;
    color: var(--ff-text); letter-spacing: 4px;
}

.menu-btn-sub {
    font-family: 'Cinzel', serif; font-size: 10px; color: var(--ff-text-dim);
    letter-spacing: 3px; margin-top: 2px;
}

.menu-footer {
    display: flex; flex-direction: column; align-items: center; gap: 4px;
}

.menu-credit {
    font-size: 10px; color: var(--ff-text-dim); letter-spacing: 3px;
}

.menu-version {
    font-size: 9px; color: rgba(138,122,90,0.5); letter-spacing: 2px;
}

.difficulty-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.9); z-index: 100;
    display: none; align-items: center; justify-content: center;
    backdrop-filter: blur(8px);
}

.difficulty-overlay.show { display: flex; }

.difficulty-content {
    text-align: center;
    animation: menuFadeIn 0.5s ease-out;
}

.diff-title {
    font-family: 'Cinzel', serif; font-size: 32px;
    background: linear-gradient(180deg, #ffd700, #d4a843);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 10px rgba(212,168,67,0.4));
    margin-bottom: 8px;
}

.diff-sub {
    font-size: 14px; color: var(--ff-text-dim); margin-bottom: 30px; letter-spacing: 2px;
}

.diff-buttons {
    display: flex; gap: 20px; justify-content: center; margin-bottom: 25px;
}

.diff-btn {
    width: 140px; padding: 20px 15px;
    background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 10px; cursor: pointer; transition: all 0.3s ease;
    display: flex; flex-direction: column; align-items: center; gap: 8px;
    color: var(--ff-text); font-family: 'Cinzel', 'Noto Serif SC', serif;
}

.diff-btn:hover {
    border-color: var(--ff-gold); transform: translateY(-3px);
    box-shadow: 0 0 20px rgba(212,168,67,0.2);
    background: rgba(26,58,92,0.5);
}

.diff-stars { font-size: 18px; color: var(--ff-gold); }

.diff-name {
    font-family: 'Noto Serif SC', serif; font-size: 18px; font-weight: 700;
    color: var(--ff-text);
}

.diff-desc {
    font-family: 'Cinzel', serif; font-size: 10px; color: var(--ff-text-dim);
    letter-spacing: 2px;
}

.diff-back {
    background: transparent; border: 1px solid var(--ff-border);
    color: var(--ff-text-dim); padding: 10px 30px; border-radius: 6px;
    cursor: pointer; font-family: 'Cinzel', 'Noto Serif SC', serif;
    font-size: 13px; transition: all 0.3s ease; letter-spacing: 2px;
}

.diff-back:hover {
    border-color: var(--ff-gold); color: var(--ff-text);
}

.ff-frame {
    position: relative; z-index: 1; width: 100%; max-width: 1280px; padding: 10px;
}

.ff-header {
    display: flex; align-items: center; justify-content: center; gap: 20px; margin-bottom: 15px;
}

.ff-header-deco {
    flex: 1; height: 2px;
    background: linear-gradient(90deg, transparent, var(--ff-gold), transparent);
    position: relative;
}

.ff-header-deco::before {
    content: '◆'; position: absolute; top: 50%; transform: translateY(-50%);
    color: var(--ff-gold); font-size: 12px;
}

.ff-header-deco.left::before { right: 0; }
.ff-header-deco.right::before { left: 0; }

.ff-title { text-align: center; display: flex; flex-direction: column; align-items: center; }

.title-cn {
    font-family: 'Noto Serif SC', serif; font-size: 28px; font-weight: 900;
    background: linear-gradient(180deg, #f0d878, #d4a843, #8b6914);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 10px rgba(212,168,67,0.3));
    letter-spacing: 12px;
}

.title-sub {
    font-family: 'Cinzel', serif; font-size: 11px;
    color: var(--ff-text-dim); letter-spacing: 6px; margin-top: 2px;
}

.game-container {
    display: flex; gap: 15px; justify-content: center; align-items: flex-start;
}

.side-panel { width: 200px; display: flex; flex-direction: column; gap: 15px; }

.player-info {
    background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 8px; padding: 12px; backdrop-filter: blur(10px);
}

.player-frame { display: flex; align-items: center; gap: 10px; margin-bottom: 8px; }

.player-avatar {
    width: 48px; height: 48px; border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
    font-size: 20px; font-weight: bold; font-family: 'Noto Serif SC', serif;
}

.player-avatar.dark {
    background: linear-gradient(135deg, #1a1a2e, #16213e);
    border: 2px solid #4a4a6a; color: #8888aa;
    box-shadow: 0 0 15px rgba(74,74,106,0.5);
}

.player-avatar.light {
    background: linear-gradient(135deg, #8b2500, #c0392b);
    border: 2px solid var(--ff-gold); color: #ffd700;
    box-shadow: 0 0 15px rgba(212,168,67,0.5);
}

.player-details { display: flex; flex-direction: column; }

.player-name { font-size: 13px; color: var(--ff-gold); font-weight: 700; }
.player-title { font-size: 10px; color: var(--ff-text-dim); margin-top: 2px; }

.player-badge {
    display: inline-block; font-size: 9px; font-family: 'Cinzel', serif;
    padding: 1px 6px; border-radius: 3px; margin-top: 3px;
    background: rgba(124,77,255,0.2); border: 1px solid rgba(124,77,255,0.4);
    color: var(--ff-purple); letter-spacing: 1px; width: fit-content;
}

.player-badge.human-badge {
    background: rgba(79,195,247,0.2); border: 1px solid rgba(79,195,247,0.4);
    color: var(--ff-crystal);
}

.captured-pieces {
    display: flex; flex-wrap: wrap; gap: 3px; min-height: 24px;
    padding-top: 6px; border-top: 1px solid rgba(212,168,67,0.1);
}

.captured-piece {
    width: 22px; height: 22px; border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
    font-size: 11px; font-weight: bold; font-family: 'Noto Serif SC', serif; opacity: 0.7;
}

.captured-piece.red {
    background: rgba(192,57,43,0.3); border: 1px solid rgba(192,57,43,0.5);
    color: var(--ff-red-light);
}

.captured-piece.black {
    background: rgba(100,100,140,0.3); border: 1px solid rgba(100,100,140,0.5);
    color: #8888cc;
}

.thinking-indicator {
    display: flex; align-items: center; justify-content: center; gap: 8px;
    padding: 10px; background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 8px;
}

.thinking-dots { display: flex; gap: 4px; }

.thinking-dots span {
    width: 6px; height: 6px; border-radius: 50%; background: var(--ff-purple);
    animation: dotPulse 1.2s ease-in-out infinite;
}

.thinking-dots span:nth-child(2) { animation-delay: 0.2s; }
.thinking-dots span:nth-child(3) { animation-delay: 0.4s; }

@keyframes dotPulse {
    0%, 100% { opacity: 0.3; transform: scale(0.8); }
    50% { opacity: 1; transform: scale(1.2); }
}

.thinking-text { font-size: 11px; color: var(--ff-text-dim); letter-spacing: 1px; }

.board-wrapper { display: flex; flex-direction: column; align-items: center; gap: 10px; }

.board-frame {
    background: linear-gradient(145deg, #1a1a2e, #0f0f1e);
    border: 2px solid var(--ff-gold-dark); border-radius: 12px; padding: 8px;
    box-shadow: 0 0 30px rgba(212,168,67,0.15), inset 0 0 30px rgba(0,0,0,0.5);
    position: relative;
}

.board-frame::before {
    content: ''; position: absolute; top: -1px; left: -1px; right: -1px; bottom: -1px;
    border-radius: 12px; border: 1px solid rgba(212,168,67,0.15); pointer-events: none;
}

.capture-fx-container {
    position: absolute; top: 0; left: 0; width: 100%; height: 100%;
    pointer-events: none; z-index: 10;
}

#chessBoard { display: block; border-radius: 8px; cursor: pointer; }

.bottom-bar {
    display: flex; align-items: center; gap: 15px;
}

.turn-indicator {
    display: flex; align-items: center; gap: 12px; padding: 8px 24px;
    background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 20px; backdrop-filter: blur(10px);
    font-size: 14px; letter-spacing: 2px;
}

.timer-container {
    display: flex; align-items: center; gap: 6px;
    background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 20px; padding: 4px 12px 4px 4px;
    backdrop-filter: blur(10px);
}

.timer-ring {
    width: 36px; height: 36px; position: relative;
}

.timer-ring svg {
    width: 36px; height: 36px; transform: rotate(-90deg);
}

.timer-bg {
    fill: none; stroke: rgba(212,168,67,0.15); stroke-width: 3;
}

.timer-progress {
    fill: none; stroke: #4fc3f7; stroke-width: 3;
    stroke-dasharray: 106.8; stroke-dashoffset: 0;
    stroke-linecap: round; transition: stroke-dashoffset 1s linear, stroke 0.3s;
}

.timer-text {
    font-family: 'Cinzel', serif; font-size: 16px; font-weight: 700;
    color: #4fc3f7; min-width: 24px; text-align: center;
    transition: color 0.3s;
}

@keyframes timerPulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.15); }
}

.turn-crystal {
    width: 10px; height: 10px; border-radius: 50%;
    animation: crystalPulse 1.5s ease-in-out infinite;
}

.red-crystal { background: var(--ff-red-light); box-shadow: 0 0 8px var(--ff-red-light); }
.black-crystal { background: #8888cc; box-shadow: 0 0 8px #8888cc; }

@keyframes crystalPulse {
    0%, 100% { opacity: 1; transform: scale(1); }
    50% { opacity: 0.5; transform: scale(0.8); }
}

.action-buttons { display: flex; flex-direction: column; gap: 8px; }

.ff-btn {
    background: linear-gradient(180deg, rgba(42,90,140,0.6), rgba(26,58,92,0.8));
    border: 1px solid var(--ff-gold-dark); color: var(--ff-text);
    padding: 10px 16px; border-radius: 6px; cursor: pointer;
    font-family: 'Cinzel', 'Noto Serif SC', serif; font-size: 13px;
    transition: all 0.3s ease;
    display: flex; align-items: center; gap: 8px; justify-content: center;
    letter-spacing: 1px; position: relative; overflow: hidden;
}

.ff-btn::before {
    content: ''; position: absolute; top: 0; left: -100%; width: 100%; height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255,255,255,0.1), transparent);
    transition: left 0.5s ease;
}

.ff-btn:hover::before { left: 100%; }

.ff-btn:hover {
    background: linear-gradient(180deg, rgba(42,90,140,0.9), rgba(26,58,92,1));
    border-color: var(--ff-gold); box-shadow: 0 0 15px rgba(212,168,67,0.3);
    transform: translateY(-1px);
}

.ff-btn:active { transform: translateY(0); }

.btn-icon { font-size: 15px; }

.battle-log {
    background: var(--ff-bg-panel); border: 1px solid var(--ff-border);
    border-radius: 8px; overflow: hidden; backdrop-filter: blur(10px);
}

.log-title {
    padding: 8px 12px; font-size: 12px; text-align: center;
    color: var(--ff-gold); border-bottom: 1px solid var(--ff-border); letter-spacing: 2px;
}

.log-content {
    padding: 8px; max-height: 250px; overflow-y: auto;
    font-size: 11px; line-height: 1.8;
}

.log-content::-webkit-scrollbar { width: 4px; }
.log-content::-webkit-scrollbar-thumb { background: var(--ff-gold-dark); border-radius: 2px; }

.log-entry {
    padding: 2px 4px; border-bottom: 1px solid rgba(212,168,67,0.05);
    display: flex; align-items: center; gap: 6px;
}

.log-entry .log-num { color: var(--ff-text-dim); font-size: 10px; min-width: 20px; }
.log-entry .log-move { color: var(--ff-text); }
.log-entry.red-move .log-move { color: var(--ff-red-light); }
.log-entry.black-move .log-move { color: #8888cc; }

.ff-footer {
    text-align: center; margin-top: 15px; font-size: 10px;
    color: var(--ff-text-dim); letter-spacing: 3px;
}

.victory-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.85); z-index: 1000;
    display: flex; align-items: center; justify-content: center;
    opacity: 0; pointer-events: none; transition: opacity 0.5s ease;
}

.victory-overlay.show { opacity: 1; pointer-events: auto; }

.victory-content { text-align: center; animation: victoryAppear 0.8s ease-out; }

@keyframes victoryAppear {
    0% { transform: scale(0.5); opacity: 0; }
    100% { transform: scale(1); opacity: 1; }
}

.victory-crystals { font-size: 30px; margin-bottom: 20px; }

.v-crystal {
    display: inline-block; animation: crystalSpin 2s linear infinite; margin: 0 10px;
}

.v-crystal.large { font-size: 50px; animation-duration: 3s; }

@keyframes crystalSpin { 0% { transform: rotateY(0deg); } 100% { transform: rotateY(360deg); } }

.victory-title {
    font-family: 'Cinzel', serif; font-size: 48px;
    background: linear-gradient(180deg, #ffd700, #d4a843, #8b6914);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    margin-bottom: 10px;
    filter: drop-shadow(0 0 20px rgba(212,168,67,0.5));
}

.victory-sub {
    font-size: 18px; color: var(--ff-text); margin-bottom: 15px; letter-spacing: 4px;
}

.victory-stats {
    font-size: 14px; color: var(--ff-text-dim); margin-bottom: 25px; letter-spacing: 2px;
}

.victory-actions { display: flex; gap: 15px; justify-content: center; }

.victory-btn { font-size: 16px; padding: 14px 30px; }

@media (max-width: 1100px) {
    .game-container { flex-direction: column; align-items: center; }
    .side-panel { width: 100%; max-width: 600px; flex-direction: row; flex-wrap: wrap; }
    .side-panel .player-info { flex: 1; min-width: 200px; }
    .action-buttons { flex-direction: row; flex-wrap: wrap; }
    .battle-log { width: 100%; }
    .log-content { max-height: 120px; }
    .logo-line-1 { font-size: 28px; letter-spacing: 6px; }
    .logo-line-2 { font-size: 36px; letter-spacing: 12px; }
    .menu-btn { width: 300px; }
}

@media (max-width: 650px) {
    #chessBoard { width: 100% !important; height: auto !important; }
    .board-frame { width: 100%; }
    .ff-frame { padding: 5px; }
    .title-cn { font-size: 22px; letter-spacing: 6px; }
    .logo-line-1 { font-size: 22px; }
    .logo-line-2 { font-size: 28px; }
    .menu-btn { width: 260px; padding: 14px 20px; }
    .diff-buttons { flex-direction: column; align-items: center; }
    .victory-title { font-size: 36px; }
}