:root {
    --bg-color: #121212;
    --primary-glow-color: #00ffff;
    --x-color: #ff00ff;
    --o-color: #00ff00;
    --text-color: #ffffff;
    --board-bg: #1a1a1a;
    --board-border: #333;
    --cell-border: #444;
    --font-family: 'Orbitron', sans-serif;
    --disabled-color: #555;
}

body.high-contrast {
    --bg-color: #000000;
    --primary-glow-color: #ffff00;
    --x-color: #ffffff;
    --o-color: #ffff00;
    --text-color: #ffffff;
    --board-bg: #111111;
    --board-border: #ffffff;
    --cell-border: #bbbbbb;
}

body.screen-flash::after {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background-color: white;
    z-index: 9999;
    pointer-events: none;
    animation: fadeOutFlash 0.5s forwards;
}

@keyframes fadeOutFlash {
    from { opacity: 0.8; }
    to { opacity: 0; }
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: var(--font-family);
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    margin: 0;
    overflow: hidden;
    transition: background-color 0.5s, color 0.5s;
}

.hidden {
    display: none !important;
}

#main-menu {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    align-items: center;
}

#main-menu button {
    padding: 20px 40px;
    font-size: 1.5rem;
    width: 300px;
    text-align: center;
}

#game-screen {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.5rem;
}

#game-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.5rem;
}

#game-title {
    font-size: 3rem;
    text-shadow: 0 0 10px var(--primary-glow-color), 0 0 20px var(--primary-glow-color), 0 0 30px var(--primary-glow-color);
    margin: 0;
}

.animate-title {
    animation: fadeInDown 1s both;
}

@keyframes fadeInDown {
    from { opacity: 0; transform: translateY(-20px); }
    to { opacity: 1; transform: translateY(0); }
}

#status-container {
    display: flex;
    align-items: center;
    gap: 1rem;
    font-size: 1.5rem;
    height: 30px;
}

#player-turn-indicator {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    transition: background-color 0.5s, box-shadow 0.5s;
}

#board-wrapper {
    position: relative;
}

#game-board {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(4, 100px);
    gap: 5px;
    background-color: var(--board-border);
    border: 2px solid var(--primary-glow-color);
    box-shadow: 0 0 15px var(--primary-glow-color);
    padding: 5px;
    position: relative;
    z-index: 1;
}

.animate-board .cell {
    animation: scaleIn 0.5s both;
}

@keyframes scaleIn {
    from { transform: scale(0); }
    to { transform: scale(1); }
}

#win-canvas {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 2;
}

.cell {
    width: 100px;
    height: 100px;
    background-color: var(--board-bg);
    border: 1px solid var(--cell-border);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 3rem;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.2s;
    position: relative;
    overflow: hidden; /* For ripple effect */
}

.cell:focus {
    outline: 2px solid var(--primary-glow-color);
    outline-offset: 2px;
}

.cell .piece {
    transform: scale(0);
    transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.cell .piece.placed {
    transform: scale(1);
}

.cell .piece.removing {
    transform: scale(0);
    transition: transform 0.3s cubic-bezier(0.6, -0.28, 0.735, 0.045);
}

.cell.X .piece {
    color: var(--x-color);
    text-shadow: 0 0 10px var(--x-color), 0 0 20px var(--x-color);
}

.cell.O .piece {
    color: var(--o-color);
    text-shadow: 0 0 10px var(--o-color), 0 0 20px var(--o-color);
}

.oldest-piece-indicator {
    position: absolute;
    width: 100%;
    height: 100%;
    border-radius: 2px;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0% { box-shadow: 0 0 0 0 rgba(255, 255, 255, 0.4); }
    70% { box-shadow: 0 0 10px 5px rgba(255, 255, 255, 0); }
    100% { box-shadow: 0 0 0 0 rgba(255, 255, 255, 0); }
}

.ripple {
    position: absolute;
    border-radius: 50%;
    background-color: rgba(255, 255, 255, 0.3);
    transform: scale(0);
    animation: ripple 0.6s linear;
}

@keyframes ripple {
    to {
        transform: scale(4);
        opacity: 0;
    }
}

.buttons-container {
    display: flex;
    gap: 1rem;
}

.buttons-container button, .modal-content button {
    padding: 10px 20px;
    font-size: 1rem;
    background-color: var(--primary-glow-color);
    color: var(--bg-color);
    border: none;
    cursor: pointer;
    transition: background-color 0.3s, box-shadow 0.3s, transform 0.2s;
    font-family: var(--font-family);
    text-transform: uppercase;
    border-radius: 5px;
}

.buttons-container button:hover, .modal-content button:hover {
    background-color: var(--x-color);
    box-shadow: 0 0 15px var(--x-color);
    transform: translateY(-2px);
}

/* Modals */
.modal {
    display: none;
    position: fixed;
    z-index: 100;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto;
    background-color: rgba(0,0,0,0.7);
    animation: fadeIn 0.3s forwards;
}

.modal-content {
    background-color: var(--board-bg);
    margin: 15% auto;
    padding: 30px;
    border: 1px solid var(--primary-glow-color);
    width: 90%;
    max-width: 500px;
    box-shadow: 0 0 20px var(--primary-glow-color);
    border-radius: 10px;
    text-align: center;
    animation: slideIn 0.3s forwards;
}

@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes fadeOut { from { opacity: 1; } to { opacity: 0; } }
@keyframes slideIn { from { transform: translateY(-50px) scale(0.95); } to { transform: translateY(0) scale(1); } }
@keyframes slideOut { from { transform: translateY(0) scale(1); } to { transform: translateY(-50px) scale(0.95); } }

.close-button {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
    position: absolute;
    top: 10px;
    right: 20px;
    transition: color 0.3s, transform 0.3s;
}

.close-button:hover, .close-button:focus {
    color: var(--x-color);
    text-decoration: none;
    cursor: pointer;
    transform: rotate(90deg);
}

#game-over-modal .modal-content {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

#game-over-message {
    font-size: 1.5rem;
    margin: 0;
}

/* Settings, Stats, Achievements */
.setting-item, #stats-content, #achievements-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    text-align: left;
}
.setting-item {
    flex-direction: row;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    border-bottom: 1px solid var(--cell-border);
}
.setting-item:last-child {
    border-bottom: none;
}
.setting-item label {
    font-size: 1.2rem;
}
.setting-item button[role="switch"] {
    width: 80px;
}
.setting-item button[role="switch"][aria-checked="true"] {
    background-color: var(--o-color);
}

.stat-line {
    display: flex;
    justify-content: space-between;
    font-size: 1.2rem;
}
.stat-line .value {
    font-weight: bold;
    color: var(--primary-glow-color);
}

.achievement {
    display: flex;
    align-items: center;
    gap: 1rem;
    opacity: 0.5;
    transition: opacity 0.5s;
}
.achievement.unlocked {
    opacity: 1;
}
.achievement .icon {
    font-size: 2rem;
}
.achievement .details h3 {
    margin: 0;
    color: var(--primary-glow-color);
}
.achievement .details p {
    margin: 0;
}
.achievement.unlocked .details h3 {
    text-shadow: 0 0 5px var(--primary-glow-color);
}

/* Toast Notifications */
#toast-container {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 9999;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.toast {
    background-color: var(--board-bg);
    color: var(--text-color);
    padding: 15px 20px;
    border-radius: 10px;
    border: 1px solid var(--primary-glow-color);
    box-shadow: 0 0 20px var(--primary-glow-color);
    animation: toastIn 0.5s forwards;
}

@keyframes toastIn {
    from { transform: translateX(100%); opacity: 0; }
    to { transform: translateX(0); opacity: 1; }
}

/* Tutorial */
#tutorial-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.8);
    z-index: 200;
    display: flex;
    align-items: center;
    justify-content: center;
}
#tutorial-overlay.hidden {
    display: none;
}
#tutorial-box {
    background-color: var(--board-bg);
    padding: 2rem;
    border-radius: 10px;
    border: 1px solid var(--primary-glow-color);
    text-align: center;
    max-width: 80%;
}
#tutorial-text {
    font-size: 1.2rem;
    margin-bottom: 1rem;
}

/* Responsive */
@media (max-width: 600px) {
    #game-title { font-size: 2rem; }
    #game-board {
        grid-template-columns: repeat(4, 70px);
        grid-template-rows: repeat(4, 70px);
    }
    .cell { width: 70px; height: 70px; font-size: 2rem; }
    .modal-content { width: 95%; margin: 25% auto; padding: 20px; }
    .buttons-container { flex-wrap: wrap; justify-content: center; }
}