:root {
    --color-yellow: #fbc400;
    --color-blue: #69c8f2;
    --color-red: #ff7272;
    --color-gray: #aaaaaa;
    --color-green: #b0d840;
    --bg-color: #f4f7f6;
    --card-bg: #ffffff;
    --text-primary: #333333;
    --text-secondary: #666666;
    --header-color: #2c3e50;
    --btn-secondary-bg: #ecf0f1;
    --btn-secondary-text: #7f8c8d;
    --border-color: #eeeeee;
    --item-border: #f9f9f9;
    --input-bg: #ffffff;
    --input-border: #dddddd;
}

body.dark-mode {
    --bg-color: #1a1a1a;
    --card-bg: #2d2d2d;
    --text-primary: #e0e0e0;
    --text-secondary: #b0b0b0;
    --header-color: #ffffff;
    --btn-secondary-bg: #3d3d3d;
    --btn-secondary-text: #b0b0b0;
    --border-color: #444444;
    --item-border: #3d3d3d;
    --input-bg: #3d3d3d;
    --input-border: #555555;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    background-color: var(--card-bg);
    max-width: 600px;
    width: 100%;
    padding: 40px;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    text-align: center;
    transition: background-color 0.3s;
}

header {
    position: relative;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
    color: var(--header-color);
}

header p {
    color: var(--text-secondary);
    margin-bottom: 30px;
}

/* Theme Toggle Button */
.theme-toggle {
    position: absolute;
    top: -20px;
    right: -20px;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 10px;
    border-radius: 50%;
    transition: background-color 0.2s;
    color: var(--text-primary);
}

.theme-toggle:hover {
    background-color: rgba(0, 0, 0, 0.05);
}

body.dark-mode .theme-toggle:hover {
    background-color: rgba(255, 255, 255, 0.05);
}

.ball-container {
    display: flex;
    justify-content: center;
    gap: 15px;
    min-height: 100px;
    margin-bottom: 40px;
    flex-wrap: wrap;
}

.placeholder-text {
    font-size: 1.2rem;
    color: var(--text-secondary);
    align-self: center;
    opacity: 0.5;
}

.ball {
    width: 60px;
    height: 60px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    color: white;
    font-weight: bold;
    font-size: 1.5rem;
    text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.3);
    box-shadow: inset -5px -5px 10px rgba(0, 0, 0, 0.2), 3px 3px 10px rgba(0, 0, 0, 0.1);
    animation: bounceIn 0.5s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

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

/* Ball Colors */
.ball.yellow { background: radial-gradient(circle at 30% 30%, #ffd700, var(--color-yellow)); }
.ball.blue { background: radial-gradient(circle at 30% 30%, #87ceeb, var(--color-blue)); }
.ball.red { background: radial-gradient(circle at 30% 30%, #ff9999, var(--color-red)); }
.ball.gray { background: radial-gradient(circle at 30% 30%, #cccccc, var(--color-gray)); }
.ball.green { background: radial-gradient(circle at 30% 30%, #c0e850, var(--color-green)); }

.controls {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-bottom: 40px;
}

.btn {
    padding: 12px 30px;
    border: none;
    border-radius: 10px;
    font-size: 1.1rem;
    font-weight: bold;
    cursor: pointer;
    transition: transform 0.2s, background-color 0.2s;
}

.btn:active {
    transform: scale(0.95);
}

.btn-primary {
    background-color: #3498db;
    color: white;
}

.btn-primary:hover {
    background-color: #2980b9;
}

.btn-secondary {
    background-color: var(--btn-secondary-bg);
    color: var(--btn-secondary-text);
}

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

.history-section {
    border-top: 1px solid var(--border-color);
    padding-top: 30px;
    text-align: left;
}

.history-section h2 {
    font-size: 1.2rem;
    margin-bottom: 15px;
    color: var(--text-secondary);
}

#history-list {
    list-style: none;
}

.history-item {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px;
    border-bottom: 1px solid var(--item-border);
    animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-5px); }
    to { opacity: 1; transform: translateY(0); }
}

.history-item .history-balls {
    display: flex;
    gap: 5px;
}

.small-ball {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    font-size: 0.75rem;
    display: flex;
    justify-content: center;
    align-items: center;
    color: white;
}

.history-date {
    font-size: 0.8rem;
    color: #999;
    margin-left: auto;
}

.contact-section {
    border-top: 1px solid var(--border-color);
    padding-top: 30px;
    margin-top: 30px;
    text-align: left;
}

.contact-section h2 {
    font-size: 1.2rem;
    margin-bottom: 20px;
    color: var(--text-secondary);
}

.contact-form {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 5px;
}

.form-group label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.form-group input,
.form-group textarea {
    padding: 12px;
    border-radius: 8px;
    border: 1px solid var(--input-border);
    background-color: var(--input-bg);
    color: var(--text-primary);
    font-family: inherit;
    font-size: 1rem;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: #3498db;
    box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.2);
}

.btn-full {
    width: 100%;
    margin-top: 10px;
}

@media (max-width: 480px) {
    .container {
        padding: 20px;
    }
    .ball {
        width: 45px;
        height: 45px;
        font-size: 1.1rem;
    }
    header h1 {
        font-size: 1.8rem;
    }
}