:root {
    /* Color Palette - Modern OKLCH */
    --bg-color: oklch(0.98 0.01 240);
    --container-bg: oklch(1 0 0);
    --text-primary: oklch(0.2 0.02 240);
    --accent-color: oklch(0.6 0.15 150); /* Green */
    --button-bg: oklch(0.55 0.18 250); /* Blue */
    --button-hover: oklch(0.45 0.2 250);
    --shadow-color: rgba(0, 0, 0, 0.1);
    --card-shadow: 0 10px 30px -5px var(--shadow-color);
    --glow-effect: 0 0 15px oklch(0.55 0.18 250 / 0.3);
}

[data-theme="dark"] {
    --bg-color: oklch(0.15 0.02 240);
    --container-bg: oklch(0.2 0.03 240);
    --text-primary: oklch(0.95 0.01 240);
    --accent-color: oklch(0.7 0.18 150);
    --button-bg: oklch(0.65 0.2 250);
    --button-hover: oklch(0.75 0.15 250);
    --shadow-color: rgba(0, 0, 0, 0.4);
    --card-shadow: 0 10px 40px -10px rgba(0, 0, 0, 0.6);
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    transition: background-color 0.4s ease, color 0.4s ease;
    /* Subtle noise texture */
    background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
    background-blend-mode: overlay;
    background-size: 150px 150px;
}

.container {
    position: relative;
    text-align: center;
    background-color: var(--container-bg);
    padding: 3rem;
    border-radius: 24px;
    box-shadow: var(--card-shadow);
    max-width: 450px;
    width: 90%;
    transition: background-color 0.4s ease, box-shadow 0.4s ease;
}

/* Theme Toggle Button */
#theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    background: transparent;
    border: 2px solid var(--text-primary);
    color: var(--text-primary);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2rem;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

#theme-toggle:hover {
    transform: rotate(15deg) scale(1.1);
    background-color: var(--text-primary);
    color: var(--container-bg);
}

h1 {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: 2.5rem;
    letter-spacing: -0.02em;
}

.numbers {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 12px;
    margin-bottom: 2.5rem;
}

.number {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 55px;
    height: 55px;
    background-color: var(--accent-color);
    color: white;
    font-size: 1.5rem;
    font-weight: 700;
    border-radius: 16px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
    transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1), background-color 0.4s ease;
}

.number:not(:empty) {
    animation: popIn 0.5s cubic-bezier(0.34, 1.56, 0.64, 1) forwards;
}

@keyframes popIn {
    0% { transform: scale(0.5); opacity: 0; }
    100% { transform: scale(1); opacity: 1; }
}

#generate {
    background-color: var(--button-bg);
    color: white;
    border: none;
    padding: 1rem 2.5rem;
    font-size: 1.1rem;
    font-weight: 600;
    border-radius: 14px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--glow-effect);
}

#generate:hover {
    background-color: var(--button-hover);
    transform: translateY(-3px);
    box-shadow: 0 8px 20px oklch(0.55 0.18 250 / 0.4);
}

#generate:active {
    transform: translateY(-1px);
}

/* Responsive adjustments */
@container (max-width: 400px) {
    .container {
        padding: 2rem;
    }
    h1 {
        font-size: 1.5rem;
    }
    .number {
        width: 45px;
        height: 45px;
        font-size: 1.2rem;
    }
}