:root {
    /* Light Theme Variables */
    --bg-color: #f4f4f4;
    --card-bg: #ffffff;
    --text-color: #333333;
    --header-bg: #111111;
    --header-text: #ffffff;
    --footer-bg: #222222;
    --footer-text: #ffffff;
    --primary-color: #0078ff;
    --primary-hover: #0056cc;
    --reset-color: #ff4444;
    --reset-hover: #cc0000;
    --shadow: rgba(0, 0, 0, 0.1);
}

[data-theme="dark"] {
    /* Dark Theme Variables */
    --bg-color: #121212;
    --card-bg: #1e1e1e;
    --text-color: #e0e0e0;
    --header-bg: #000000;
    --header-text: #ffffff;
    --footer-bg: #1a1a1a;
    --footer-text: #aaaaaa;
    --shadow: rgba(255, 255, 255, 0.05);
}

body {
    font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, sans-serif;
    text-align: center;
    margin: 0;
    padding: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: background-color 0.3s, color 0.3s;
}

header {
    background-color: var(--header-bg);
    color: var(--header-text);
    padding: 40px 20px;
    position: relative;
}

header h1 {
    font-size: 2rem;
    margin-bottom: 10px;
}

#theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    padding: 10px 15px;
    font-size: 14px;
    border-radius: 20px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    cursor: pointer;
    transition: transform 0.2s;
}

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

section {
    padding: 20px;
}

.box {
    background: var(--card-bg);
    margin: 20px auto;
    padding: 30px;
    width: 90%;
    max-width: 800px;
    border-radius: 20px;
    box-shadow: 0px 4px 20px var(--shadow);
    transition: background-color 0.3s, box-shadow 0.3s;
}

button {
    padding: 14px 28px;
    font-size: 1rem;
    font-weight: 600;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    margin: 8px;
    transition: background-color 0.2s, transform 0.1s;
}

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

button:active {
    transform: translateY(1px);
}

.reset-btn {
    background-color: var(--reset-color);
}

.reset-btn:hover {
    background-color: var(--reset-hover);
}

.ball {
    display: inline-flex;
    justify-content: center;
    align-items: center;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    color: white;
    font-weight: bold;
    font-size: 1.1rem;
    margin: 8px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
}

footer {
    background: var(--footer-bg);
    color: var(--footer-text);
    padding: 20px;
    margin-top: 50px;
    font-size: 0.9rem;
}

/* Form Styling */
.form-group {
    text-align: left;
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    font-weight: 600;
    margin-bottom: 8px;
    font-size: 0.95rem;
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: 12px 15px;
    border-radius: 10px;
    border: 1px solid #ddd;
    background-color: var(--card-bg);
    color: var(--text-color);
    font-size: 1rem;
    box-sizing: border-box;
    transition: border-color 0.2s, box-shadow 0.2s;
}

[data-theme="dark"] .form-group input,
[data-theme="dark"] .form-group textarea {
    border-color: #444;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 8px rgba(0, 120, 255, 0.2);
}

.submit-btn {
    width: 100%;
    margin-top: 10px;
    font-size: 1.1rem;
}

/* Responsive Optimization */
@media (max-width: 600px) {
    header h1 {
        font-size: 1.5rem;
    }

    .box {
        padding: 20px;
    }

    button {
        width: 100%;
        margin: 5px 0;
    }

    .ball {
        width: 45px;
        height: 45px;
        font-size: 1rem;
    }
}