/* ==================== Global Styles ==================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #00b8d4;
    --primary-dark: #0097a7;
    --cool-accent: #00e5ff;
    --secondary-color: #6c757d;
    --success-color: #28a745;
    --danger-color: #dc3545;
    --warning-color: #ffc107;
    --info-color: #00acc1;
    --light-color: #f8f9fa;
    --dark-color: #263238;
    --border-color: #dee2e6;
    --shadow: 0 2px 8px rgba(0,184,212,0.1);
    --shadow-lg: 0 4px 12px rgba(0,184,212,0.15);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: var(--light-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* ==================== Navigation ==================== */
.navbar {
    background-color: white;
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.navbar .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 20px;
}

.nav-brand a {
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--primary-color);
    text-decoration: none;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 1rem;
    align-items: center;
}

.nav-menu a {
    color: #333;
    text-decoration: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    transition: background-color 0.3s;
}

.nav-menu a:hover {
    background-color: var(--light-color);
}

.nav-toggle {
    display: none;
    flex-direction: column;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.nav-toggle span {
    width: 25px;
    height: 3px;
    background-color: #333;
    margin: 3px 0;
    transition: 0.3s;
}

/* ==================== Main Content ==================== */
.main-content {
    flex: 1;
    padding: 2rem 0;
}

/* ==================== Footer ==================== */
.footer {
    background-color: white;
    border-top: 1px solid var(--border-color);
    padding: 1.5rem 0;
    text-align: center;
    color: var(--secondary-color);
    margin-top: auto;
}

/* ==================== Buttons ==================== */
.btn {
    display: inline-block;
    padding: 0.5rem 1.5rem;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    text-decoration: none;
    font-size: 1rem;
    transition: all 0.3s;
    text-align: center;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background-color: var(--primary-dark);
}

.btn-success {
    background-color: var(--success-color);
    color: white;
}

.btn-success:hover {
    background-color: #218838;
}

.btn-danger {
    background-color: var(--danger-color);
    color: white;
}

.btn-danger:hover {
    background-color: #c82333;
}

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

.btn-secondary:hover {
    background-color: #5a6268;
}

.btn-logout {
    background-color: var(--danger-color) !important;
    color: white !important;
}

.btn-logout:hover {
    background-color: #c82333 !important;
}

.btn-sm {
    padding: 0.25rem 0.75rem;
    font-size: 0.875rem;
}

.btn-block {
    display: block;
    width: 100%;
}

/* ==================== Flash Messages ==================== */
.flash-messages {
    margin-bottom: 1.5rem;
}

.alert {
    padding: 1rem;
    margin-bottom: 1rem;
    border-radius: 4px;
    position: relative;
}

.alert-success {
    background-color: #d4edda;
    color: #155724;
    border: 1px solid #c3e6cb;
}

.alert-danger {
    background-color: #f8d7da;
    color: #721c24;
    border: 1px solid #f5c6cb;
}

.alert-warning {
    background-color: #fff3cd;
    color: #856404;
    border: 1px solid #ffeeba;
}

.alert-info {
    background-color: #d1ecf1;
    color: #0c5460;
    border: 1px solid #bee5eb;
}

.alert-close {
    position: absolute;
    top: 0.5rem;
    right: 1rem;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: inherit;
    opacity: 0.7;
}

.alert-close:hover {
    opacity: 1;
}

/* ==================== Cards ==================== */
.card {
    background-color: white;
    border-radius: 8px;
    box-shadow: var(--shadow);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
}

.card-header {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
    margin-bottom: 1rem;
}

.card-title {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
}

.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-bottom: 1.5rem;
}

.stat-card {
    background-color: white;
    border-radius: 8px;
    box-shadow: var(--shadow);
    padding: 1.5rem;
    text-align: center;
    transition: transform 0.3s;
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.stat-value {
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.stat-label {
    color: var(--secondary-color);
    font-size: 0.9rem;
}

/* ==================== Forms ==================== */
.form-group {
    margin-bottom: 1.5rem;
}

.form-label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.form-control {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-size: 1rem;
    transition: border-color 0.3s;
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
}

textarea.form-control {
    min-height: 100px;
    resize: vertical;
}

.form-error {
    color: var(--danger-color);
    font-size: 0.875rem;
    margin-top: 0.25rem;
}

.form-check {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.form-check input[type="checkbox"] {
    width: 1.25rem;
    height: 1.25rem;
    cursor: pointer;
}

/* ==================== Tables ==================== */
.table-container {
    overflow-x: auto;
}

.table {
    width: 100%;
    border-collapse: collapse;
    background-color: white;
    border-radius: 8px;
    overflow: hidden;
}

.table th,
.table td {
    padding: 1rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.table th {
    background-color: var(--light-color);
    font-weight: 600;
}

.table tbody tr:hover {
    background-color: var(--light-color);
}

/* ==================== Status Badges ==================== */
.badge {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    border-radius: 12px;
    font-size: 0.875rem;
    font-weight: 500;
}

.badge-draft {
    background-color: #e9ecef;
    color: #495057;
}

.badge-sent {
    background-color: #d1ecf1;
    color: #0c5460;
}

.badge-paid {
    background-color: #d4edda;
    color: #155724;
}

.badge-overdue {
    background-color: #f8d7da;
    color: #721c24;
}

/* ==================== Page Header ==================== */
.page-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

.page-title {
    font-size: 2rem;
    color: #333;
}

/* ==================== Hero Section ==================== */
.hero {
    text-align: center;
    padding: 4rem 0;
}

.hero h1 {
    font-size: 3rem;
    margin-bottom: 1rem;
    color: #333;
}

.hero p {
    font-size: 1.25rem;
    color: var(--secondary-color);
    margin-bottom: 2rem;
}

.hero .btn {
    margin: 0.5rem;
}

/* ==================== Responsive Design ==================== */
@media (max-width: 768px) {
    .nav-menu {
        display: none;
        flex-direction: column;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background-color: white;
        box-shadow: var(--shadow);
        padding: 1rem;
    }

    .nav-menu.active {
        display: flex;
    }

    .nav-toggle {
        display: flex;
    }

    .page-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 1rem;
    }

    .card-grid {
        grid-template-columns: 1fr;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .hero p {
        font-size: 1rem;
    }

    .table {
        font-size: 0.875rem;
    }

    .table th,
    .table td {
        padding: 0.5rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 15px;
    }

    .btn {
        padding: 0.5rem 1rem;
        font-size: 0.875rem;
    }

    .stat-value {
        font-size: 1.5rem;
    }
}

/* ==================== Utility Classes ==================== */
.text-center {
    text-align: center;
}

.text-right {
    text-align: right;
}

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }

.d-flex {
    display: flex;
}

.justify-between {
    justify-content: space-between;
}

.align-center {
    align-items: center;
}

.gap-1 { gap: 0.5rem; }
.gap-2 { gap: 1rem; }

/* ==================== Pagination ==================== */
.pagination {
    display: flex;
    justify-content: center;
    list-style: none;
    margin-top: 2rem;
    gap: 0.5rem;
}

.pagination a {
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    text-decoration: none;
    color: #333;
}

.pagination a:hover {
    background-color: var(--light-color);
}

.pagination .active a {
    background-color: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

/* ==================== Loading Spinner ==================== */
.spinner {
    border: 3px solid var(--light-color);
    border-top: 3px solid var(--primary-color);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 1s linear infinite;
    margin: 2rem auto;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}