:root {
    --bg-color: #f0f2f5;
    --text-color: #333;
    --container-bg: white;
    --h1-color: #4a4a4a;
    --primary-color: #4CAF50;
    --primary-hover: #45a049;
    --number-bg: #4CAF50;
    --number-text: white;
    --shadow-color: rgba(0, 0, 0, 0.1);
    --btn-shadow: rgba(0, 0, 0, 0.2);
    --transition-speed: 0.3s;
}

body.dark-theme {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --container-bg: #1e1e1e;
    --h1-color: #ffffff;
    --primary-color: #81c784;
    --primary-hover: #a5d6a7;
    --number-bg: #81c784;
    --number-text: #121212;
    --shadow-color: rgba(0, 0, 0, 0.5);
    --btn-shadow: rgba(0, 0, 0, 0.6);
}

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

.container {
    text-align: center;
    background-color: var(--container-bg);
    padding: 40px;
    border-radius: 20px;
    box-shadow: 0 10px 30px var(--shadow-color);
    transition: background-color var(--transition-speed), box-shadow var(--transition-speed);
    max-width: 500px;
    width: 90%;
}

h1 {
    margin-bottom: 30px;
    font-size: 2.2em;
    color: var(--h1-color);
    transition: color var(--transition-speed);
}

.numbers {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 15px;
    margin-bottom: 40px;
    min-height: 60px;
}

.number {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 60px;
    height: 60px;
    border-radius: 50%;
    background-color: var(--number-bg);
    color: var(--number-text);
    font-size: 1.5em;
    font-weight: bold;
    box-shadow: 0 4px 10px var(--btn-shadow);
    transition: transform 0.3s ease-out, background-color var(--transition-speed), color var(--transition-speed);
    animation: popIn 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

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

.controls {
    display: flex;
    flex-direction: column;
    gap: 20px;
    align-items: center;
}

#generate {
    background-color: var(--primary-color);
    color: var(--number-text);
    border: none;
    padding: 15px 35px;
    font-size: 1.1em;
    font-weight: 600;
    border-radius: 12px;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.2s, box-shadow 0.3s;
    box-shadow: 0 4px 15px var(--btn-shadow);
}

#generate:hover {
    background-color: var(--primary-hover);
    transform: translateY(-3px);
    box-shadow: 0 6px 20px var(--btn-shadow);
}

#generate:active {
    transform: translateY(0);
}

#theme-toggle {
    background: none;
    border: 2px solid var(--primary-color);
    color: var(--primary-color);
    padding: 8px 16px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.9em;
    transition: all 0.3s;
}

#theme-toggle:hover {
    background-color: var(--primary-color);
    color: var(--number-text);
}