:root {
    --bg-color: #f0f0f2;
    --text-color: #333;
    --card-bg: #fff;
    --number-bg: #fff;
    --btn-bg: #4CAF50;
    --btn-hover: #45a049;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.dark-mode {
    --bg-color: #1a1a2e;
    --text-color: #e0e0e0;
    --card-bg: #16213e;
    --number-bg: #0f3460;
    --btn-bg: #e94560;
    --btn-hover: #cf3a52;
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.5);
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: background-color 0.3s, color 0.3s;
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
}

#theme-btn {
    padding: 8px 16px;
    cursor: pointer;
    border: none;
    background-color: var(--card-bg);
    color: var(--text-color);
    border-radius: 20px;
    box-shadow: var(--shadow);
    transition: transform 0.2s;
}

#theme-btn:active {
    transform: scale(0.95);
}

.container {
    text-align: center;
    padding: 2rem;
    background-color: var(--card-bg);
    border-radius: 15px;
    box-shadow: var(--shadow);
    max-width: 500px;
    width: 90%;
}

h1 {
    margin-bottom: 2rem;
}

#sets-container {
    display: flex;
    flex-direction: column;
    gap: 15px;
    margin-bottom: 2rem;
}

.numbers-container {
    display: flex;
    justify-content: center;
    gap: 8px;
    padding: 10px;
    background-color: var(--bg-color);
    border-radius: 10px;
}

.number {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background-color: var(--number-bg);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 18px;
    font-weight: bold;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

#generate-btn {
    padding: 12px 30px;
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    border: none;
    background-color: var(--btn-bg);
    color: white;
    border-radius: 25px;
    box-shadow: var(--shadow);
    transition: background-color 0.2s, transform 0.1s;
}

#generate-btn:hover {
    background-color: var(--btn-hover);
}

#generate-btn:active {
    transform: translateY(2px);
}