:root {
    --bg-gradient: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    --container-bg: white;
    --text-color: #333;
    --display-color: #4a90e2;
    --btn-bg: #4a90e2;
    --btn-hover: #357abd;
}

[data-theme="dark"] {
    --bg-gradient: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    --container-bg: #1f4068;
    --text-color: #e94560;
    --display-color: #0f3460;
    --btn-bg: #e94560;
    --btn-hover: #c31432;
    background-color: #1a1a2e;
}

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

.container {
    text-align: center;
    background: var(--container-bg);
    padding: 3rem;
    border-radius: 20px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
    transition: background 0.3s ease, transform 0.3s ease;
}

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

#number-display {
    font-size: 6rem;
    font-weight: 800;
    margin: 1.5rem 0;
    color: var(--display-color);
    min-height: 120px;
}

button#generate-btn {
    padding: 15px 40px;
    font-size: 1.5rem;
    font-weight: bold;
    cursor: pointer;
    background-color: var(--btn-bg);
    color: white;
    border: none;
    border-radius: 50px;
    transition: transform 0.2s, background-color 0.2s;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

button#generate-btn:hover {
    background-color: var(--btn-hover);
    transform: translateY(-2px);
}

.theme-btn {
    position: absolute;
    top: 20px;
    right: 20px;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    border: none;
    background: var(--container-bg);
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    cursor: pointer;
    font-size: 1.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
}

.theme-btn:hover {
    transform: scale(1.1);
}

[data-theme="dark"] #number-display {
    color: #fff;
}