:root {
    --primary-color: #4CAF50; /* Green for check-in */
    --primary-dark: #388E3C;
    --secondary-color: #2196F3; /* Blue for check-out */
    --secondary-dark: #1976D2;
    --bg-color: #f7f9fc;
    --text-main: #1C1E21;
    --card-bg: rgba(255, 255, 255, 0.9);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: 'Pretendard', sans-serif;
    background: linear-gradient(135deg, #e0eafc, #cfdef3);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    color: var(--text-main);
}

.app-container {
    background: var(--card-bg);
    width: 100%;
    max-width: 600px;
    height: 100vh;
    max-height: 850px;
    border-radius: 24px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    display: flex;
    flex-direction: column;
    padding: 30px;
    backdrop-filter: blur(10px);
}

.header h1 {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 900;
    color: #333;
    margin-bottom: 20px;
    letter-spacing: -1px;
}

.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 40px;
}

.time-card {
    text-align: center;
    background: #fff;
    padding: 30px;
    border-radius: 20px;
    box-shadow: 0 8px 16px rgba(0,0,0,0.05);
    width: 100%;
}

.date {
    font-size: 1.5rem;
    color: #666;
    margin-bottom: 10px;
    font-weight: 700;
}

.time {
    font-size: 5rem;
    font-weight: 900;
    color: #222;
    line-height: 1;
    letter-spacing: -2px;
}

.button-group {
    display: flex;
    flex-direction: column;
    gap: 20px;
    width: 100%;
}

.btn {
    border: none;
    border-radius: 24px;
    padding: 30px 20px;
    font-size: 3rem;
    font-weight: 900;
    color: white;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 20px;
    box-shadow: 0 6px 15px rgba(0,0,0,0.15);
    transition: transform 0.1s ease, box-shadow 0.1s ease;
    width: 100%;
}

.btn:active {
    transform: scale(0.96);
    box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
}

.btn-secondary {
    background: linear-gradient(135deg, var(--secondary-color), var(--secondary-dark));
}

.icon {
    font-size: 3.5rem;
}

.status-message {
    min-height: 60px;
    font-size: 1.5rem;
    font-weight: 700;
    text-align: center;
    padding: 15px 20px;
    border-radius: 12px;
    opacity: 0;
    transition: opacity 0.3s ease;
    background: #e8f5e9;
    color: #2e7d32;
    width: 100%;
}

.status-message.show {
    opacity: 1;
}

.status-message.error {
    background: #ffebee;
    color: #c62828;
}

/* Responsiveness handling */
@media (max-width: 400px) {
    .time { font-size: 4rem; }
    .btn { font-size: 2.2rem; padding: 20px; }
    .icon { font-size: 2.5rem; }
    .app-container { padding: 20px; }
    .status-message { font-size: 1.2rem; }
}