:root {
    --bg-color: #f0f2f5;
    --container-bg: #ffffff;
    --text-color: #333;
    --heading-color: #1877f2;
    --number-bg: #e4e6eb;
    --number-text: #1c1e21;
    --btn-bg: #1877f2;
    --btn-text: #ffffff;
    --shadow-color: rgba(0, 0, 0, 0.1);
}

body.dark-mode {
    --bg-color: #18191a;
    --container-bg: #242526;
    --text-color: #e4e6eb;
    --heading-color: #2e89ff;
    --number-bg: #3a3b3c;
    --number-text: #e4e6eb;
    --btn-bg: #2e89ff;
    --btn-text: #ffffff;
    --shadow-color: rgba(0, 0, 0, 0.5);
}

body {
    font-family: 'Helvetica Neue', 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 0.3s ease, color 0.3s ease;
}

.container {
    background-color: var(--container-bg);
    padding: 40px;
    border-radius: 16px;
    box-shadow: 0 10px 30px var(--shadow-color);
    text-align: center;
    transition: transform 0.3s ease, background-color 0.3s ease, box-shadow 0.3s ease;
    position: relative;
}

.container:hover {
    transform: translateY(-5px);
}

h1 {
    margin-bottom: 20px;
    font-size: 2.2em;
    color: var(--heading-color);
    text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.1);
    transition: color 0.3s ease;
}

.controls {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin-bottom: 25px;
    flex-wrap: wrap;
}

.control-group {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    gap: 5px;
}

.control-group label {
    font-size: 0.9em;
    font-weight: bold;
    color: var(--text-color);
    opacity: 0.8;
}

.control-group select {
    padding: 8px 12px;
    border-radius: 6px;
    border: 1px solid var(--number-bg);
    background-color: var(--container-bg);
    color: var(--text-color);
    font-size: 1em;
    cursor: pointer;
    transition: border-color 0.3s ease;
}

.control-group select:focus {
    outline: none;
    border-color: var(--heading-color);
}

.sets-wrapper {
    display: flex;
    flex-direction: column;
    gap: 15px;
    margin-bottom: 30px;
    max-height: 400px;
    overflow-y: auto;
    padding-right: 5px;
}

.numbers-container {
    display: flex;
    justify-content: center;
    gap: 10px;
    padding: 10px;
    background-color: var(--bg-color);
    border-radius: 12px;
    transition: background-color 0.3s ease;
}

.number {
    width: 45px;
    height: 45px;
    background-color: var(--number-bg);
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2em;
    font-weight: bold;
    color: var(--number-text);
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
}

#generate-btn {
    background-color: var(--btn-bg);
    color: var(--btn-text);
    border: none;
    padding: 15px 30px;
    font-size: 1.2em;
    border-radius: 8px;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.2s ease;
    box-shadow: 0 4px 12px var(--shadow-color);
}

#generate-btn:hover {
    filter: brightness(1.1);
    transform: translateY(-2px);
}

#generate-btn:active {
    transform: translateY(1px);
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    background: none;
    border: none;
    font-size: 1.5em;
    cursor: pointer;
    color: var(--text-color);
    transition: color 0.3s ease;
}