:root {
    --bg-color: #f0f0f0;
    --container-bg: #ffffff;
    --text-color: #333333;
    --number-bg: #eeeeee;
    --number-text: #333333;
    --button-bg: #4CAF50;
    --button-text: #ffffff;
    --button-hover: #45a049;
    --shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
    --transition-speed: 0.3s;
}

body.dark-mode {
    --bg-color: #121212;
    --container-bg: #1e1e1e;
    --text-color: #e0e0e0;
    --number-bg: #333333;
    --number-text: #ffffff;
    --button-bg: #66bb6a;
    --button-text: #000000;
    --button-hover: #81c784;
    --shadow: 0 4px 15px rgba(0, 0, 0, 0.5);
}

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

.container {
    text-align: center;
    background-color: var(--container-bg);
    padding: 2.5rem;
    border-radius: 20px;
    box-shadow: var(--shadow);
    transition: background-color var(--transition-speed), box-shadow var(--transition-speed);
    width: 90%;
    max-width: 400px;
    position: relative;
}

.theme-toggle {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1.5rem;
    padding: 0.5rem;
    color: var(--text-color);
    transition: color var(--transition-speed), transform 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}

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

h1 {
    margin-bottom: 2rem;
    font-size: 1.8rem;
}

.numbers {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.8rem;
    margin-bottom: 2rem;
    min-height: 50px;
}

.number {
    width: 45px;
    height: 45px;
    border-radius: 50%;
    background-color: var(--number-bg);
    color: var(--number-text);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.1rem;
    font-weight: bold;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    animation: popIn 0.3s ease-out forwards;
}

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

#generate {
    padding: 0.8rem 1.5rem;
    font-size: 1.1rem;
    font-weight: 600;
    border: none;
    border-radius: 12px;
    background-color: var(--button-bg);
    color: var(--button-text);
    cursor: pointer;
    transition: background-color 0.2s, transform 0.1s;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

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

#generate:active {
    transform: translateY(2px);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}