:root {
    --primary: #3498db;
    --primary-dark: #2980b9;
    --success: #27ae60;
    --warning: #f39c12;
    --danger: #e74c3c;
    --bg: #f8f9fa;
    --text: #2c3e50;
    --shadow: 0 4px 6px rgba(0,0,0,0.1);
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: var(--bg);
    margin: 0;
    padding: 10px;
    color: var(--text);
    line-height: 1.6;
}

.container {
    max-width: 600px;
    margin: 10px auto;
    background: #fff;
    padding: 20px;
    border-radius: 16px;
    box-shadow: var(--shadow);
}

.nav {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-bottom: 25px;
    padding-bottom: 15px;
    border-bottom: 1px solid #eee;
}

.nav a {
    text-decoration: none;
    color: var(--primary);
    font-weight: 600;
    font-size: 0.9em;
    padding: 5px 10px;
    border-radius: 8px;
    transition: background 0.2s;
}

.nav a:hover {
    background: #f0f7ff;
}

.task-card {
    background: #fff;
    border: 1px solid #edf2f7;
    padding: 20px;
    border-radius: 12px;
    margin-bottom: 20px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.02);
}

.announcement-box {
    background: #ebf8ff;
    border-left: 4px solid var(--primary);
    padding: 15px;
    border-radius: 8px;
    margin-bottom: 15px;
}

.btn {
    display: inline-block;
    padding: 12px 24px;
    background-color: var(--success);
    color: white;
    text-decoration: none;
    border-radius: 10px;
    border: none;
    font-weight: 600;
    cursor: pointer;
    text-align: center;
    transition: opacity 0.2s;
    width: 100%;
}

.btn-done { background-color: var(--primary); }
.btn:active { opacity: 0.8; }

table { width: 100%; border-collapse: collapse; margin-top: 10px; font-size: 0.9em; }
th, td { padding: 12px 8px; text-align: left; border-bottom: 1px solid #f1f1f1; }
th { color: #7f8c8d; font-weight: 600; }

/* Calendar Special Styles */
.calendar-grid { display: grid; grid-template-columns: repeat(7, 1fr); gap: 4px; }
.calendar-day { 
    border: 1px solid #f0f0f0; 
    padding: 5px; 
    min-height: 70px; 
    border-radius: 6px; 
    font-size: 0.8em; 
    cursor: pointer;
}
.active-day { background: #fff; transition: background 0.2s; }
.active-day:hover { background: #f0f7ff; }
.today-day { border: 2px solid var(--primary); background: #f0f7ff; }
.task-dot { 
    height: 6px; width: 6px; 
    background: var(--success); 
    border-radius: 50%; 
    margin: 4px auto 0;
}
.done-task { 
    text-decoration: line-through; 
    color: #a0aec0; 
    opacity: 0.7; 
}

/* Modal Styling */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0; top: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.5);
    backdrop-filter: blur(2px);
}
.modal-content {
    background: #fff;
    margin: 20% auto;
    padding: 25px;
    width: 85%;
    max-width: 400px;
    border-radius: 16px;
    position: relative;
}
.close-modal {
    position: absolute;
    right: 15px; top: 10px;
    font-size: 24px;
    cursor: pointer;
}

@media (max-width: 480px) {
    .container { padding: 15px; }
    h1 { font-size: 1.5em; }
}