:root {
    --primary-color: #4a90e2;
    --background-color: #f0f2f5;
    --text-color: #333;
    --container-bg: #fff;
    --border-radius: 8px;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --white: #fff;
}

[data-theme='dark'] {
    --background-color: #1a1a1a;
    --text-color: #f0f2f5;
    --container-bg: #2d2d2d;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    background-color: var(--container-bg);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    text-align: center;
    transition: background-color 0.3s ease;
    max-width: 600px;
    width: 90%;
    margin: 2rem;
}

h1 {
    color: var(--primary-color);
    margin-bottom: 2rem;
}

.theme-toggle {
    position: absolute;
    top: 1rem;
    right: 1rem;
}

#toggle-btn {
    background: none;
    border: 1px solid var(--primary-color);
    color: var(--primary-color);
    padding: 0.5rem 1rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 0.8rem;
    transition: all 0.3s ease;
}

#toggle-btn:hover {
    background-color: var(--primary-color);
    color: var(--white);
}

.numbers {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 15px;
    margin-bottom: 2rem;
    max-height: 60vh;
    overflow-y: auto;
    padding: 10px;
}

.set {
    display: flex;
    gap: 10px;
    padding: 10px;
    border-bottom: 1px solid var(--background-color);
}

.set:last-child {
    border-bottom: none;
}

.number {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: var(--white);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2rem;
    font-weight: bold;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.controls {
    display: flex;
    justify-content: center;
    gap: 10px;
    flex-wrap: wrap;
}

.btn {
    background-color: var(--primary-color);
    color: var(--white);
    border: none;
    padding: 0.8rem 1.5rem;
    font-size: 0.9rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.1s ease;
    box-shadow: var(--shadow);
}

.btn:hover {
    background-color: #357abd;
}

.btn:active {
    transform: translateY(1px);
}