:root {
    --primary: #2c3e50; --secondary: #34495e; --accent: #3498db;
    --success: #27ae60; --danger: #e74c3c; --light: #f4f6f7;
    --white: #fff; --text: #333; --border: #ddd;
    --shadow: 0 2px 5px rgba(0,0,0,0.1); --radius: 5px;
    --font: 'Segoe UI', sans-serif;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: var(--font); background: var(--light); color: var(--text); line-height: 1.6; }
a { text-decoration: none; color: var(--accent); }
ul { list-style: none; }

/* Layout & Common */
.main-content { max-width: 1200px; margin: 30px auto; padding: 0 20px; min-height: 80vh; }
.page-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 20px; border-bottom: 2px solid var(--border); padding-bottom: 10px; }
.page-header h1 { color: var(--primary); }
.section-divider { margin: 40px 0; border: 0; border-top: 1px solid var(--border); }

/* Navbar */
.main-navbar { background: var(--primary); color: var(--white); padding: 1rem 0; box-shadow: var(--shadow); }
.nav-container { max-width: 1200px; margin: 0 auto; display: flex; justify-content: space-between; align-items: center; padding: 0 20px; }
.brand-logo { font-size: 1.5rem; font-weight: bold; color: var(--white); }
.nav-links { display: flex; gap: 20px; }
.nav-item { color: #ecf0f1; font-weight: 500; transition: color 0.3s; }
.nav-item:hover { color: var(--accent); }

/* Components: Cards, Containers */
.stat-card, .form-wrapper, .login-container, .table-container {
    background: var(--white); padding: 30px; border-radius: var(--radius); box-shadow: var(--shadow);
}
.stat-card { text-align: center; border-top: 5px solid var(--accent); }
.stat-card h3 { font-size: 1.2rem; color: var(--secondary); margin-bottom: 10px; }
.stat-number { font-size: 2.5rem; font-weight: bold; color: var(--primary); }

/* Dashboard */
.dashboard-header { text-align: center; margin-bottom: 40px; }
.dashboard-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 20px; }

/* Forms */
.form-wrapper, .login-container { max-width: 600px; margin: 0 auto; }
.login-wrapper { display: flex; justify-content: center; align-items: center; min-height: 70vh; }
.login-container { max-width: 400px; padding: 40px; }
.form-header, .login-container h2 { text-align: center; margin-bottom: 20px; color: var(--primary); }
.styled-form .form-group { margin-bottom: 15px; }
.styled-form label { display: block; margin-bottom: 5px; font-weight: 600; color: var(--secondary); }
.form-input, .form-select, .search-input {
    width: 100%; padding: 10px; border: 1px solid var(--border); border-radius: var(--radius); font-size: 1rem;
}
.form-input:focus, .form-select:focus { outline: none; border-color: var(--accent); }
.form-actions, .login-footer { text-align: center; margin-top: 20px; }

/* Buttons */
.btn, .btn-logout {
    display: inline-block; padding: 10px 20px; border: none; border-radius: var(--radius);
    cursor: pointer; font-size: 1rem; transition: background 0.3s; color: var(--white);
}
.btn-primary { background: var(--accent); }
.btn-primary:hover { background: #2980b9; }
.btn-secondary { background: var(--secondary); }
.btn-secondary:hover { background: #2c3e50; }
.btn-logout { background: var(--danger); padding: 8px 15px; font-size: 0.9rem; }
.btn-logout:hover { background: #c0392b; }
.btn-block { width: 100%; display: block; }

/* Tables */
.table-container { padding: 20px; overflow-x: auto; }
.data-table { width: 100%; border-collapse: collapse; margin-top: 10px; }
.data-table th, .data-table td { padding: 12px 15px; text-align: left; border-bottom: 1px solid var(--border); }
.data-table th { background: var(--primary); color: var(--white); font-weight: 600; }
.data-table tr:hover { background: #f1f1f1; }
.action-links a { margin-right: 10px; font-size: 0.9rem; }
.link-edit { color: var(--accent); }
.link-delete { color: var(--danger); }
.empty-table { text-align: center; color: #7f8c8d; font-style: italic; }

/* Search & Alerts */
.search-bar-container { margin-bottom: 20px; display: flex; justify-content: flex-end; }
.search-form { display: flex; gap: 10px; }
.search-input { width: 250px; }
.messages { margin-bottom: 20px; }
.alert { padding: 15px; border-radius: var(--radius); margin-bottom: 10px; color: var(--white); }
.alert.success, .status-returned { background-color: var(--success); } /* Status returned uses text color usually, check logic */
.alert.error, .alert.warning { background-color: var(--danger); }
.alert.info { background-color: var(--accent); }

/* Status Text Colors (override bg from alert if needed) */
span.status-returned { background: none; color: var(--success); }
span.status-issued { color: #f39c12; font-weight: bold; }
td.due-status { color: var(--danger); font-weight: bold; }