:root {
    --bg-color: #f4f7f6;
    --text-color: #333;
    --card-bg: #fff;
    --primary-color: #4a90e2;
    --secondary-color: #f39c12;
    --danger-color: #e74c3c;
    --success-color: #2ecc71;
    --border-radius: 12px;
}

body.dark-mode {
    --bg-color: #121212;
    --text-color: #f1f1f1;
    --card-bg: #1e1e1e;
    --primary-color: #3f7cb5;
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 0;
    text-align: center; /* Center aligned as requested */
    transition: background-color 0.3s, color 0.3s;
}

.screen {
    display: none;
}
.screen.active {
    display: block;
}

/* Login Container */
.login-container {
    background-color: var(--card-bg);
    max-width: 400px;
    margin: 100px auto;
    padding: 30px;
    border-radius: var(--border-radius);
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

.form-group {
    margin-bottom: 15px;
}
.form-group input {
    width: 90%;
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: var(--border-radius);
    text-align: center;
}

button {
    padding: 10px 20px;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-weight: bold;
    margin: 5px;
}
.btn-primary { background-color: var(--primary-color); color: white; }
.btn-secondary { background-color: #7f8c8d; color: white; }
.btn-danger { background-color: var(--danger-color); color: white; }
.btn-success { background-color: var(--success-color); color: white; }

/* Navbar */
.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: var(--card-bg);
    padding: 15px 30px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}

.nav-links a {
    margin: 0 10px;
    text-decoration: none;
    color: var(--primary-color);
    font-weight: bold;
}

.main-content {
    padding: 30px;
}

/* Cards */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
}
.card {
    background-color: var(--card-bg);
    padding: 20px;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.5);
    justify-content: center;
    align-items: center;
}
.modal.active {
    display: flex;
}
.modal-content {
    background: var(--card-bg);
    padding: 20px;
    border-radius: var(--border-radius);
    min-width: 300px;
}