:root {
    --background-color: #f0f2f5;
    --text-color: #333;
    --button-background: #4CAF50;
    --button-text: white;
    --number-background: #f0f0f0;
    --number-text: #333;
}

body.dark-theme {
    --background-color: #333;
    --text-color: #f0f2f5;
    --button-background: #6a0dad; /* A darker, purplish hue */
    --button-text: #f0f2f5;
    --number-background: #555;
    --number-text: #f0f2f5;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: var(--background-color);
    color: var(--text-color);
    transition: background-color 0.3s, color 0.3s;
}