:root {
    /* Dark Mode Colors */
    --dark-bg-primary: #121212;
    --dark-bg-secondary: #1e1e1e;
    --dark-bg-tertiary: #2c2c2c;
    --dark-accent-color: #bb86fc;
    --dark-text-color: #ffffff;

    /* Light Mode Colors (Elegant Dual Shades) */
    --light-bg-primary: #f0f4f8; /* Soft light blue-gray */
    --light-bg-secondary: #dbe3eb; /* Slightly darker shade for elements - improved visibility */
    --light-bg-tertiary: #c2ccd4; /* Even darker for borders/accents */
    --light-accent-color: #4a90e2; /* A pleasant blue */
    --light-text-color: #333333;

    --border-radius: 10px;
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

/* Default (Light Mode) Colors */
body {
    background: var(--light-bg-primary);
    color: var(--light-text-color);
    font-family: var(--font-family);
    margin: 0;
    overflow: hidden;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Dark Mode Overrides */
html.dark body {
    background: var(--dark-bg-primary);
    color: var(--dark-text-color);
}

h1 {
    font-size: 3rem;
    margin-top: 0; /* Removed margin-top as it's handled by parent flex container */
    margin-bottom: 1rem;
    text-shadow: 0 0 10px var(--light-accent-color);
    transition: text-shadow 0.3s ease;
}

html.dark h1 {
    text-shadow: 0 0 10px var(--dark-accent-color);
}

#game-board {
    display: grid;
    grid-template-columns: repeat(3, 100px);
    grid-template-rows: repeat(3, 100px);
    gap: 10px;
    background: rgba(0, 0, 0, 0.05);
    padding: 20px;
    border-radius: var(--border-radius);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(0, 0, 0, 0.1);
    transition: background 0.3s ease, border 0.3s ease;
}

html.dark #game-board {
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.2);
}

.cell {
    width: 100px;
    height: 100px;
    background: var(--light-bg-secondary);
    border: 2px solid var(--light-bg-tertiary); /* Added border for better definition */
    border-radius: var(--border-radius);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 4rem;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.2s ease, color 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease;
    color: var(--light-accent-color);
    text-shadow: none;
}

html.dark .cell {
    background: var(--dark-bg-secondary);
    border: 2px solid var(--dark-bg-tertiary); /* Added border for better definition */
    color: var(--dark-accent-color);
    text-shadow: 0 0 5px var(--dark-accent-color);
}

.cell:hover {
    background-color: var(--light-bg-tertiary);
    transform: scale(1.05);
    box-shadow: 0 0 15px var(--light-accent-color); /* Neon glow for light mode */
}

html.dark .cell:hover {
    background-color: var(--dark-bg-tertiary);
    box-shadow: 0 0 15px var(--dark-accent-color); /* Neon glow for dark mode */
}

.cell.x::before, .cell.o::before {
    opacity: 0;
    animation: fadeIn 0.5s forwards;
}

.cell.x::before {
    content: 'X';
}

.cell.o::before {
    content: 'O';
}

@keyframes fadeIn {
    from { opacity: 0; transform: scale(0.5); }
    to { opacity: 1; transform: scale(1); }
}

.controls {
    margin-top: 2rem;
    background: rgba(0, 0, 0, 0.05);
    padding: 1rem 1.5rem;
    border-radius: var(--border-radius);
    border: 1px solid rgba(0, 0, 0, 0.1);
    transition: background 0.3s ease, border 0.3s ease;
}

html.dark .controls {
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.2);
}

.controls label {
    margin-right: 10px;
    font-size: 1.2rem;
}

#difficulty {
    background: var(--light-bg-tertiary);
    color: var(--light-text-color);
    border: 1px solid var(--light-accent-color);
    border-radius: 5px;
    padding: 0.5rem;
    font-size: 1rem;
    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease;
}

html.dark #difficulty {
    background: var(--dark-bg-tertiary);
    color: var(--dark-text-color);
    border-color: var(--dark-accent-color);
}

#winningMessage {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.9);
    justify-content: center;
    align-items: center;
    color: white;
    font-size: 5rem;
    flex-direction: column;
    backdrop-filter: blur(5px);
}

#winningMessage.show {
    display: flex;
    animation: fadeIn 0.5s;
}

#winningMessage div {
    margin-bottom: 1rem;
}

#restartButton {
    font-size: 2rem;
    background-color: var(--light-accent-color);
    border: none;
    border-radius: var(--border-radius);
    padding: 0.5em 1em;
    cursor: pointer;
    color: var(--light-text-color);
    transition: background-color 0.3s, transform 0.2s, color 0.3s ease;
}

html.dark #restartButton {
    background-color: var(--dark-accent-color);
    color: var(--dark-bg-primary);
}

#restartButton:hover {
    background-color: #3a7bd5; /* A slightly darker blue for hover */
    transform: scale(1.05);
}

html.dark #restartButton:hover {
    background-color: #a764fc;
}

.watermark {
    position: fixed;
    bottom: 10px;
    right: 10px;
    font-size: 1rem;
    color: rgba(0, 0, 0, 0.3);
    pointer-events: none;
    transition: color 0.3s ease;
}

html.dark .watermark {
    color: rgba(255, 255, 255, 0.3);
}

/* Disable board clicks during computer's turn */
#game-board.disabled-board {
    pointer-events: none;
    opacity: 0.7;
}