/* --- THEME VARIABLES --- */
:root {
    --bg-color: #1a1a2e;
    --container-color: #16213e;
    --cell-color: #0f3460;
    --accent-color: #e94560;
    --text-color: #ffffff;
    --player-x-color: #53a8b6;
    --player-o-color: #e94560;
    --line-color: #ffc107;
    --font-family: 'Poppins', sans-serif;
    --blob-color-1: #e94560;
    --blob-color-2: #53a8b6;
    --blob-color-3: #8a3ffc;
}
[data-theme="light"] {
    --bg-color: #f8f9fa;
    --container-color: #ffffff;
    --cell-color: #e9ecef;
    --accent-color: #20c997;
    --text-color: #212529;
    --player-x-color: #20c997;
    --player-o-color: #fd7e14;
    --line-color: #0d6efd;
    --blob-color-1: #20c997;
    --blob-color-2: #fd7e14;
    --blob-color-3: #0d6efd;
}

/* --- SPLASH SCREEN --- */
#splash-screen {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background-color: var(--bg-color);
    display: flex; justify-content: center; align-items: center;
    z-index: 10000;
    transition: opacity 0.5s ease-out;
}
#splash-screen.fade-out { opacity: 0; }
.splash-title {
    font-size: clamp(2em, 8vw, 4em); color: var(--accent-color);
    text-shadow: 0 0 15px rgba(255,255,255,0.3);
    animation: splash-text-animation 2s ease-out forwards;
}
@keyframes splash-text-animation {
    0% { opacity: 0; transform: scale(0.8) translateY(20px); }
    80% { opacity: 1; transform: scale(1.05) translateY(0); }
    100% { opacity: 1; transform: scale(1) translateY(0); }
}

/* --- LAYOUT & GLOBAL STYLES --- */
body {
    margin: 0; font-family: var(--font-family); background-color: var(--bg-color);
    color: var(--text-color); display: flex; justify-content: center;
    align-items: center; height: 100vh; overflow: hidden; padding: 10px;
    box-sizing: border-box; transition: background-color 0.3s ease, color 0.3s ease;
}
#boardSizeSelection, #mainMenu, #gameContainer {
    position: relative; text-align: center; background-color: var(--container-color);
    padding: 1em; border-radius: 15px; box-shadow: 0 10px 30px rgba(0, 0, 0, 0.15);
    width: 100%; max-width: 480px; transition: background-color 0.3s ease; z-index: 2;
}
h1 { font-size: clamp(1.8em, 7vmin, 2.5em); color: var(--accent-color); margin: 0 0 0.5em 0; transition: color 0.3s ease; }
h2 { font-size: clamp(1.1em, 4vmin, 1.3em); margin-top: 0.5em; margin-bottom: 0.5em; min-height: 1.2em; }
button { padding: 10px 20px; font-size: 0.9em; font-family: var(--font-family); color: #ffffff; background-color: var(--accent-color); border: none; border-radius: 8px; cursor: pointer; transition: all 0.2s ease; margin: 0.5em; }
button:hover { transform: translateY(-2px); box-shadow: 0 4px 10px rgba(0,0,0,0.2); }
.hidden { display: none !important; }

/* --- ANIMATED BACKGROUND --- */
.background-container { position: fixed; top: 0; left: 0; width: 100%; height: 100%; overflow: hidden; z-index: 1; }
.blob { position: absolute; border-radius: 50%; filter: blur(100px); opacity: 0.4; }
.blob:nth-child(1) { width: 400px; height: 400px; background: var(--blob-color-1); top: -150px; left: -150px; animation: move-blob-1 10s infinite alternate; }
.blob:nth-child(2) { width: 300px; height: 300px; background: var(--blob-color-2); bottom: -100px; right: -100px; animation: move-blob-2 12s infinite alternate; }
.blob:nth-child(3) { width: 250px; height: 250px; background: var(--blob-color-3); bottom: 50px; left: -150px; animation: move-blob-3 14s infinite alternate-reverse; }
@keyframes move-blob-1 { from { transform: translate(0, 0) rotate(0deg); } to { transform: translate(200px, 100px) rotate(180deg); } }
@keyframes move-blob-2 { from { transform: translate(0, 0) rotate(0deg); } to { transform: translate(-150px, -150px) rotate(-180deg); } }
@keyframes move-blob-3 { from { transform: translateY(0px); } to { transform: translateY(-200px); } }

/* --- THEME SWITCHER --- */
.theme-switcher { position: absolute; top: 20px; right: 25px; z-index: 100; }
.theme-switcher input { display: none; }
.theme-switcher .slider { position: relative; display: flex; align-items: center; width: 50px; height: 26px; background-color: var(--cell-color); border-radius: 26px; cursor: pointer; transition: background-color 0.3s ease; }
.theme-switcher .slider::before { content: ''; position: absolute; top: 3px; left: 3px; width: 20px; height: 20px; background-color: white; border-radius: 50%; box-shadow: 0 0 2px rgba(0,0,0,0.2); transition: transform 0.3s ease; }
.theme-switcher input:checked + .slider { background-color: var(--accent-color); }
.theme-switcher input:checked + .slider::before { transform: translateX(24px); }
.theme-switcher .icon { position: absolute; font-size: 14px; transition: opacity 0.3s ease, transform 0.3s ease; }
.sun-icon { right: 5px; opacity: 0; transform: scale(0); }
.moon-icon { left: 5px; opacity: 1; transform: scale(1); }
.theme-switcher input:checked + .slider .sun-icon { opacity: 1; transform: scale(1); }
.theme-switcher input:checked + .slider .moon-icon { opacity: 0; transform: scale(0); }

/* --- NAME ENTRY & SCOREBOARD --- */
.input-group { margin-bottom: 0.8em; display: flex; flex-direction: column; align-items: center; }
.input-group label { margin-bottom: 0.4em; font-weight: 600; font-size: 0.9em; }
.input-group input { width: 80%; padding: 8px; border-radius: 5px; border: 2px solid var(--accent-color); background-color: var(--cell-color); color: var(--text-color); font-family: var(--font-family); text-align: center; font-size: 1em; transition: all 0.3s ease; }
#scoreboard { display: flex; justify-content: space-around; margin-bottom: 0.5em; }
.score-card { background-color: var(--cell-color); padding: 0.4em 0.8em; border-radius: 8px; width: 40%; transition: background-color 0.3s ease; }
.score-name { display: block; font-weight: 600; font-size: 0.8em; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.score-value { display: block; font-size: 1.5em; font-weight: 700; }
#player1Score .score-value { color: var(--player-x-color); }
#player2Score .score-value { color: var(--player-o-color); }

/* --- DYNAMIC GAME BOARD & CELLS --- */
#gameBoard { position: relative; display: grid; grid-template-columns: repeat(var(--grid-size, 3), 1fr); width: 100%; max-width: 400px; margin: 0.5em auto; border: 5px solid var(--accent-color); border-radius: 10px; overflow: hidden; transition: border-color 0.3s ease; }
.cell { width: 100%; padding-bottom: 100%; position: relative; border: 2px solid var(--container-color); background-color: var(--cell-color); transition: all 0.3s ease; }
.cell::before { content: ''; position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); font-size: clamp(1.5rem, calc(20vw / var(--grid-size, 3)), 4rem); font-weight: 700; }
.cell:hover { background-color: rgba(0, 0, 0, 0.05); cursor: pointer; }
.cell.x::before { content: 'X'; color: var(--player-x-color); }
.cell.o::before { content: 'O'; color: var(--player-o-color); }

/* --- GAME BUTTONS --- */
.button-group { display: flex; justify-content: center; align-items: center; margin-top: 0.5em; }