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

body {
    font-family: 'Arial', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
}

.screen {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}

.hidden {
    display: none !important;
}

/* Login Screen */
.login-container {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
    text-align: center;
    min-width: 300px;
}

.login-container h1 {
    margin-bottom: 2rem;
    color: #333;
}

.login-container input {
    width: 100%;
    padding: 0.8rem;
    margin: 0.5rem 0;
    border: 1px solid #ddd;
    border-radius: 5px;
    font-size: 1rem;
}

.login-container button {
    width: 100%;
    padding: 0.8rem;
    margin: 0.5rem 0;
    border: none;
    border-radius: 5px;
    font-size: 1rem;
    cursor: pointer;
    transition: background-color 0.3s;
}

#login-btn {
    background: #4CAF50;
    color: white;
}

#login-btn:hover {
    background: #45a049;
}

#register-btn {
    background: #2196F3;
    color: white;
}

#register-btn:hover {
    background: #1976D2;
}

#auth-message {
    margin-top: 1rem;
    padding: 0.5rem;
    border-radius: 5px;
}

.error {
    background: #ffebee;
    color: #c62828;
}

.success {
    background: #e8f5e8;
    color: #2e7d32;
}

/* Main Menu */
.menu-container {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
    min-width: 500px;
    max-width: 600px;
}

.menu-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid #eee;
}

.menu-section {
    margin-bottom: 2rem;
}

.menu-section h2 {
    margin-bottom: 1rem;
    color: #333;
    font-size: 1.2rem;
}

.menu-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
}

.menu-btn {
    padding: 1rem;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s;
    font-weight: 500;
}

.menu-btn.primary {
    background: #4CAF50;
    color: white;
}

.menu-btn.primary:hover {
    background: #45a049;
    transform: translateY(-2px);
}

.menu-btn.secondary {
    background: #2196F3;
    color: white;
}

.menu-btn.secondary:hover {
    background: #1976D2;
    transform: translateY(-2px);
}

.menu-btn:not(.primary):not(.secondary) {
    background: #f5f5f5;
    color: #333;
    border: 1px solid #ddd;
}

.menu-btn:not(.primary):not(.secondary):hover {
    background: #e0e0e0;
    transform: translateY(-2px);
}
/* Game Screen */
#game-screen {
    flex-direction: column;
    align-items: stretch;
    padding: 1rem;
}

.game-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: white;
    padding: 1rem;
    border-radius: 10px;
    margin-bottom: 1rem;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.player-info {
    display: flex;
    gap: 2rem;
    align-items: center;
}

.player {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 0.5rem 1rem;
    border-radius: 8px;
    min-width: 120px;
}

.white-player {
    background: #f8f8f8;
    border: 2px solid #ddd;
}

.black-player {
    background: #333;
    color: white;
    border: 2px solid #666;
}

.player.active {
    border-color: #4CAF50;
    box-shadow: 0 0 10px rgba(76, 175, 80, 0.3);
}

.game-controls button, .game-controls select {
    margin-left: 0.5rem;
    padding: 0.5rem 1rem;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 0.9rem;
}

.game-controls button {
    background: #4CAF50;
    color: white;
}

.game-controls button:hover {
    background: #45a049;
}

.game-controls select {
    background: white;
    border: 1px solid #ddd;
}

.ai-only {
    display: none;
}

.ai-mode .ai-only {
    display: inline-block;
}

.online-only {
    display: none;
}

.online-mode .online-only {
    display: block;
}

.game-container {
    display: flex;
    gap: 1rem;
    justify-content: center;
    align-items: flex-start;
    width: 100%;
    max-width: 1400px;
    margin: 0 auto;
}

.game-sidebar {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    min-width: 250px;
    flex-shrink: 0;
}

.game-sidebar.left {
    order: 1;
}

.game-sidebar.right {
    order: 3;
}

#chess-board {
    order: 2;
    display: grid;
    grid-template-columns: repeat(8, 60px);
    grid-template-rows: repeat(8, 60px);
    border: 3px solid #8B4513;
    border-radius: 5px;
    box-shadow: 0 5px 20px rgba(0,0,0,0.3);
    background: white;
    flex-shrink: 0;
    transition: transform 0.3s ease-in-out;
}

/* Local mode indicator */
.local-mode #chess-board {
    box-shadow: 0 5px 20px rgba(76, 175, 80, 0.4);
    border-color: #4CAF50;
}

.game-info {
    background: white;
    padding: 1rem;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

#current-player {
    font-weight: bold;
    margin-bottom: 1rem;
    padding: 0.5rem;
    background: #f5f5f5;
    border-radius: 5px;
    text-align: center;
}

#game-status {
    margin-bottom: 1rem;
    padding: 0.5rem;
    border-radius: 5px;
    text-align: center;
    font-weight: bold;
}

#connection-status {
    padding: 0.5rem;
    border-radius: 5px;
    text-align: center;
    font-size: 0.9rem;
    margin-bottom: 1rem;
}

#connection-status.connected {
    background: #e8f5e8;
    color: #2e7d32;
}

#connection-status.disconnected {
    background: #ffebee;
    color: #c62828;
}

.game-won {
    background: #e8f5e8;
    color: #2e7d32;
}

.game-draw {
    background: #fff3e0;
    color: #f57c00;
}

.ai-thinking {
    background: #e3f2fd;
    color: #1976d2;
    animation: pulse 1.5s infinite;
}

.captured-pieces {
    margin-bottom: 1rem;
}

.captured {
    margin: 0.5rem 0;
    min-height: 40px;
    padding: 0.5rem;
    background: #f5f5f5;
    border-radius: 5px;
    display: flex;
    flex-wrap: wrap;
    gap: 2px;
}

.captured-piece {
    width: 30px;
    height: 30px;
    font-size: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* Chess Board */
.square {
    width: 60px;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 40px;
    cursor: pointer;
    position: relative;
    transition: background-color 0.2s;
}

.square.light {
    background-color: #f0d9b5;
}

.square.dark {
    background-color: #b58863;
}

.square.selected {
    background-color: #7fb069 !important;
    box-shadow: inset 0 0 0 3px #5a8a4a;
}

.square.valid-move {
    background-color: #9fd3c7 !important;
}

.square.valid-move::after {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    background: #2e7d32;
    border-radius: 50%;
    opacity: 0.7;
}

.square.capture-move {
    background-color: #ffab91 !important;
}

.square.capture-move::after {
    content: '';
    position: absolute;
    width: 50px;
    height: 50px;
    border: 3px solid #d32f2f;
    border-radius: 50%;
    opacity: 0.7;
}

.square.in-check {
    background-color: #ff5252 !important;
    animation: pulse 1s infinite;
}

@keyframes pulse {
    0% { opacity: 1; }
    50% { opacity: 0.7; }
    100% { opacity: 1; }
}

/* Move History */
.move-history {
    background: white;
    padding: 1rem;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    max-height: 300px;
    overflow-y: auto;
}

.move-history h3 {
    margin-bottom: 1rem;
    color: #333;
    text-align: center;
}

#moves-list {
    font-family: monospace;
    font-size: 0.9rem;
}

.move-pair {
    display: flex;
    margin-bottom: 0.2rem;
}

.move-number {
    width: 30px;
    font-weight: bold;
    color: #666;
}

.move {
    flex: 1;
    padding: 0 0.5rem;
}

/* Chat */
#game-chat {
    background: white;
    padding: 1rem;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    height: 300px;
    display: flex;
    flex-direction: column;
}

#game-chat h3 {
    margin-bottom: 1rem;
    color: #333;
    text-align: center;
}

#chat-messages {
    flex: 1;
    overflow-y: auto;
    border: 1px solid #eee;
    border-radius: 5px;
    padding: 0.5rem;
    margin-bottom: 1rem;
    font-size: 0.9rem;
}

.chat-message {
    margin-bottom: 0.5rem;
    padding: 0.3rem;
    border-radius: 3px;
}

.chat-message.own {
    background: #e3f2fd;
    text-align: right;
}

.chat-message.opponent {
    background: #f5f5f5;
}

.chat-message .username {
    font-weight: bold;
    font-size: 0.8rem;
    color: #666;
}

.chat-input {
    display: flex;
    gap: 0.5rem;
}

#chat-input {
    flex: 1;
    padding: 0.5rem;
    border: 1px solid #ddd;
    border-radius: 5px;
    font-size: 0.9rem;
}

#send-chat-btn {
    padding: 0.5rem 1rem;
    background: #2196F3;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 0.9rem;
}

#send-chat-btn:hover {
    background: #1976D2;
}

/* Modals */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
}

.modal-content {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
    min-width: 300px;
    max-width: 90vw;
    max-height: 90vh;
    overflow-y: auto;
}

.modal-content.large {
    min-width: 500px;
}

.modal-content h3 {
    margin-bottom: 1.5rem;
    color: #333;
    text-align: center;
}

.modal-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    margin-top: 1.5rem;
}

.modal-buttons button {
    padding: 0.8rem 1.5rem;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1rem;
}

.modal-buttons button:first-child {
    background: #4CAF50;
    color: white;
}

.modal-buttons button:last-child {
    background: #f44336;
    color: white;
}

.close-modal {
    width: 100%;
    padding: 0.8rem;
    background: #666;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    margin-top: 1rem;
}

/* Promotion Modal */
.promotion-pieces {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
}

.promotion-btn {
    padding: 1rem;
    border: 2px solid #ddd;
    border-radius: 8px;
    background: white;
    cursor: pointer;
    font-size: 1.2rem;
    transition: all 0.3s;
}

.promotion-btn:hover {
    border-color: #4CAF50;
    background: #f8f8f8;
    transform: scale(1.05);
}

/* Friends Modal */
.friends-tabs {
    display: flex;
    margin-bottom: 1rem;
    border-bottom: 1px solid #eee;
}

.tab-btn {
    flex: 1;
    padding: 0.8rem;
    border: none;
    background: none;
    cursor: pointer;
    font-size: 1rem;
    color: #666;
    border-bottom: 2px solid transparent;
}

.tab-btn.active {
    color: #4CAF50;
    border-bottom-color: #4CAF50;
}

.tab-content {
    min-height: 300px;
}

.friend-item, .request-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    border: 1px solid #eee;
    border-radius: 8px;
    margin-bottom: 0.5rem;
}

.friend-info {
    display: flex;
    flex-direction: column;
}

.friend-name {
    font-weight: bold;
    margin-bottom: 0.2rem;
}

.friend-elo {
    font-size: 0.9rem;
    color: #666;
}

.friend-actions {
    display: flex;
    gap: 0.5rem;
}

.friend-actions button {
    padding: 0.4rem 0.8rem;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.8rem;
}

.invite-btn {
    background: #4CAF50;
    color: white;
}

.remove-btn {
    background: #f44336;
    color: white;
}

.accept-btn {
    background: #4CAF50;
    color: white;
}

.decline-btn {
    background: #f44336;
    color: white;
}

/* Leaderboard */
.leaderboard-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    border: 1px solid #eee;
    border-radius: 8px;
    margin-bottom: 0.5rem;
}

.leaderboard-rank {
    font-weight: bold;
    font-size: 1.2rem;
    color: #4CAF50;
    min-width: 40px;
}

.leaderboard-info {
    flex: 1;
    margin-left: 1rem;
}

.leaderboard-name {
    font-weight: bold;
    margin-bottom: 0.2rem;
}

.leaderboard-stats {
    font-size: 0.9rem;
    color: #666;
}

.leaderboard-elo {
    font-weight: bold;
    font-size: 1.1rem;
    color: #333;
}

/* Responsive Design */
@media (max-width: 1200px) {
    .game-container {
        flex-direction: column;
        align-items: center;
    }
    
    .game-sidebar {
        flex-direction: row;
        min-width: auto;
        width: 100%;
        max-width: 600px;
        justify-content: space-around;
    }
    
    .game-sidebar.left {
        order: 2;
    }
    
    .game-sidebar.right {
        order: 3;
    }
    
    #chess-board {
        order: 1;
        margin-bottom: 1rem;
    }
    
    .game-info, .move-history, #game-chat {
        flex: 1;
        margin: 0 0.5rem;
    }
}

@media (max-width: 768px) {
    .menu-container {
        min-width: 90vw;
        padding: 1.5rem;
    }
    
    .menu-buttons {
        grid-template-columns: 1fr;
    }
    
    .game-header {
        flex-direction: column;
        gap: 1rem;
    }
    
    .player-info {
        flex-direction: column;
        gap: 1rem;
    }
    
    .game-sidebar {
        flex-direction: column;
    }
    
    #chess-board {
        grid-template-columns: repeat(8, 45px);
        grid-template-rows: repeat(8, 45px);
    }
    
    .square {
        width: 45px;
        height: 45px;
        font-size: 30px;
    }
    
    .modal-content {
        margin: 1rem;
        padding: 1.5rem;
    }
    
    .modal-content.large {
        min-width: auto;
        width: 90vw;
    }
    
    .promotion-pieces {
        grid-template-columns: 1fr;
    }
    
    .friends-tabs {
        flex-direction: column;
    }
    
    .tab-btn {
        border-bottom: none;
        border-right: 2px solid transparent;
    }
    
    .tab-btn.active {
        border-right-color: #4CAF50;
        border-bottom-color: transparent;
    }
}

@media (max-width: 480px) {
    #chess-board {
        grid-template-columns: repeat(8, 35px);
        grid-template-rows: repeat(8, 35px);
    }
    
    .square {
        width: 35px;
        height: 35px;
        font-size: 24px;
    }
    
    .menu-btn {
        padding: 0.8rem;
        font-size: 0.9rem;
    }
    
    .game-controls button,
    .game-controls select {
        padding: 0.4rem 0.8rem;
        font-size: 0.8rem;
    }
}

/* ============================================================
   Enhancement styles
   ============================================================ */

/* CSS variables for board themes */
:root {
    --light-square: #f0d9b5;
    --dark-square:  #b58863;
}

.square.light { background-color: var(--light-square); }
.square.dark  { background-color: var(--dark-square);  }

/* Last-move highlight */
.square.last-move {
    background-color: rgba(255, 255, 0, 0.45) !important;
}

/* Check pulse */
.square.in-check-pulse {
    background-color: rgba(220, 50, 50, 0.7) !important;
    animation: checkPulse 0.8s ease-in-out infinite alternate;
}
@keyframes checkPulse {
    from { background-color: rgba(220, 50, 50, 0.5); }
    to   { background-color: rgba(220, 50, 50, 0.85); }
}

/* Dark mode */
body.dark-mode {
    background: #1a1a2e;
    color: #e0e0e0;
}
body.dark-mode .menu-container,
body.dark-mode .game-header,
body.dark-mode .game-sidebar,
body.dark-mode .modal-content {
    background: #16213e;
    color: #e0e0e0;
}
body.dark-mode .move-history,
body.dark-mode .game-info {
    background: #0f3460;
    color: #e0e0e0;
}

/* Timer */
.timer {
    font-size: 1.6rem;
    font-weight: bold;
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.05em;
    padding: 4px 12px;
    border-radius: 8px;
    background: #e8e8e8;
    color: #222;
    margin-top: 4px;
    min-width: 80px;
    text-align: center;
    display: block;
    transition: background 0.3s, color 0.3s;
    opacity: 0.45;
}
.timer:empty { display: none; }
.timer.timer-active {
    opacity: 1;
    box-shadow: 0 0 0 2px #4caf50;
}
.timer.low-time {
    background: #ff5722;
    color: white;
    opacity: 1;
    animation: timerPulse 1s infinite;
}
@keyframes timerPulse {
    0%, 100% { opacity: 1; }
    50%       { opacity: 0.6; }
}
.black-player .timer {
    background: #555;
    color: #fff;
}
.black-player .timer.low-time {
    background: #ff5722;
    color: white;
}

/* Move history controls */
.move-history-controls {
    display: flex;
    gap: 6px;
    margin-top: 8px;
    flex-wrap: wrap;
}
.move-history-controls button {
    flex: 1;
    padding: 6px 10px;
    font-size: 0.8rem;
    background: #667eea;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}
.move-history-controls button:hover { background: #5568d3; }

/* Analysis panel */
#analysis-panel {
    margin-top: 12px;
    padding: 12px;
    background: #f9f9f9;
    border-radius: 8px;
    font-size: 0.85rem;
}
body.dark-mode #analysis-panel { background: #0f3460; }
#analysis-panel h3 { margin-bottom: 8px; }
.analysis-summary table { width: 100%; border-collapse: collapse; margin-bottom: 10px; }
.analysis-summary td,
.analysis-summary th { padding: 3px 6px; text-align: center; }
.analysis-moves { line-height: 1.8; }
.analysis-move  { margin-right: 4px; cursor: default; }
#close-analysis-btn {
    margin-top: 8px;
    padding: 5px 12px;
    background: #aaa;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

/* Settings modal */
.settings-section {
    margin-bottom: 16px;
    padding-bottom: 12px;
    border-bottom: 1px solid #eee;
}
.settings-section h4 { margin-bottom: 8px; color: #555; }
.theme-buttons { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 8px; }
.theme-btn {
    padding: 6px 14px;
    border: 2px solid #ddd;
    border-radius: 6px;
    cursor: pointer;
    background: white;
    font-size: 0.85rem;
}
.theme-btn:hover { border-color: #667eea; }
.toggle-label { display: flex; align-items: center; gap: 8px; margin: 6px 0; cursor: pointer; }
.settings-section label { display: block; margin: 6px 0; font-size: 0.9rem; }
.settings-section input[type="range"] { width: 100%; margin-top: 4px; }
.settings-section select { padding: 4px 8px; border-radius: 4px; border: 1px solid #ddd; }

/* Tournament invite badge */
.badge {
    display: inline-block;
    background: #f44336;
    color: white;
    border-radius: 50%;
    font-size: 0.7rem;
    font-weight: bold;
    min-width: 18px;
    height: 18px;
    line-height: 18px;
    text-align: center;
    padding: 0 4px;
    margin-left: 4px;
    vertical-align: middle;
}