/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #2563eb;
    --primary-dark: #1e40af;
    --secondary-color: #64748b;
    --success-color: #10b981;
    --danger-color: #ef4444;
    --warning-color: #f59e0b;
    --info-color: #3b82f6;
    --bg-color: #f8fafc;
    --text-color: #1e293b;
    --border-color: #e2e8f0;
    --white: #ffffff;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    font-size: 16px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    margin-bottom: 1rem;
    font-weight: 600;
    line-height: 1.2;
}

h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.25rem; }

p {
    margin-bottom: 1rem;
}

/* Navigation */
.navbar {
    background-color: var(--white);
    border-bottom: 1px solid var(--border-color);
    padding: 0;
    box-shadow: var(--shadow);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 1rem;
}

.nav-brand a {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    padding: 1rem 0;
    display: block;
}

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

.nav-menu li {
    margin-left: 1rem;
}

.nav-menu a {
    color: var(--text-color);
    text-decoration: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    transition: background-color 0.2s;
    display: block;
}

.nav-menu a:hover,
.nav-menu a.active {
    background-color: var(--bg-color);
    color: var(--primary-color);
}

.nav-menu .nav-right {
    margin-left: 2rem;
    display: flex;
    align-items: center;
    gap: 1rem;
}

.nav-menu .username {
    color: var(--secondary-color);
    font-size: 0.9rem;
}

.btn-logout {
    background-color: var(--danger-color);
    color: var(--white) !important;
    padding: 0.5rem 1rem;
    border-radius: 4px;
}

.btn-logout:hover {
    background-color: #dc2626 !important;
}

/* Container */
.container {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
    min-height: calc(100vh - 200px);
}

/* Cards */
.card {
    background-color: var(--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;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.card-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin: 0;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 0.5rem 1rem;
    border: none;
    border-radius: 4px;
    font-size: 1rem;
    font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: all 0.2s;
    text-align: center;
}

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

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

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

.btn-secondary:hover {
    background-color: #475569;
}

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

.btn-success:hover {
    background-color: #059669;
}

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

.btn-danger:hover {
    background-color: #dc2626;
}

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

.btn-group {
    display: flex;
    gap: 0.5rem;
}

/* Forms */
.form-group {
    margin-bottom: 1rem;
}

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

.form-control {
    width: 100%;
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-size: 1rem;
    transition: border-color 0.2s;
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-control:disabled {
    background-color: var(--bg-color);
    cursor: not-allowed;
}

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

select.form-control {
    cursor: pointer;
}

.form-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
}

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

table {
    width: 100%;
    border-collapse: collapse;
}

table thead {
    background-color: var(--bg-color);
}

table th,
table td {
    padding: 0.75rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

table th {
    font-weight: 600;
    color: var(--secondary-color);
    font-size: 0.875rem;
    text-transform: uppercase;
}

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

/* Alerts */
.alert {
    padding: 1rem;
    border-radius: 4px;
    margin-bottom: 1rem;
}

.alert-success {
    background-color: #d1fae5;
    color: #065f46;
    border: 1px solid #a7f3d0;
}

.alert-error,
.alert-danger {
    background-color: #fee2e2;
    color: #991b1b;
    border: 1px solid #fecaca;
}

.alert-warning {
    background-color: #fef3c7;
    color: #92400e;
    border: 1px solid #fde68a;
}

.alert-info {
    background-color: #dbeafe;
    color: #1e40af;
    border: 1px solid #bfdbfe;
}

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

.badge-draft {
    background-color: #e2e8f0;
    color: #475569;
}

.badge-issued {
    background-color: #dbeafe;
    color: #1e40af;
}

.badge-paid {
    background-color: #d1fae5;
    color: #065f46;
}

.badge-part-paid {
    background-color: #fef3c7;
    color: #92400e;
}

.badge-overdue {
    background-color: #fee2e2;
    color: #991b1b;
}

.badge-void {
    background-color: #f3f4f6;
    color: #6b7280;
}

/* Stats Cards */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.stat-card {
    background-color: var(--white);
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

.stat-label {
    color: var(--secondary-color);
    font-size: 0.875rem;
    text-transform: uppercase;
    margin-bottom: 0.5rem;
}

.stat-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-color);
}

/* Login Page */
.login-container {
    max-width: 400px;
    margin: 5rem auto;
    padding: 0 1rem;
}

.login-card {
    background-color: var(--white);
    padding: 2rem;
    border-radius: 8px;
    box-shadow: var(--shadow-lg);
}

.login-card h1 {
    text-align: center;
    margin-bottom: 2rem;
    color: var(--primary-color);
}

/* Invoice Items Table */
.invoice-items-table {
    margin: 1rem 0;
}

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

.invoice-items-table input {
    width: 100%;
}

.btn-remove-item {
    background: none;
    border: none;
    color: var(--danger-color);
    cursor: pointer;
    font-size: 1.2rem;
}

.btn-remove-item:hover {
    color: #dc2626;
}

/* Totals Section */
.totals-section {
    max-width: 400px;
    margin-left: auto;
    margin-top: 1rem;
    border-top: 2px solid var(--border-color);
    padding-top: 1rem;
}

.totals-row {
    display: flex;
    justify-content: space-between;
    padding: 0.5rem 0;
}

.totals-row.grand-total {
    font-size: 1.25rem;
    font-weight: 700;
    border-top: 2px solid var(--border-color);
    margin-top: 0.5rem;
    padding-top: 0.75rem;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 3rem 1rem;
    color: var(--secondary-color);
}

.empty-state-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

/* Footer */
.footer {
    background-color: var(--white);
    border-top: 1px solid var(--border-color);
    padding: 1.5rem 0;
    margin-top: 3rem;
}

.footer-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
    text-align: center;
    color: var(--secondary-color);
    font-size: 0.875rem;
}

/* Responsive */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        padding: 0.5rem 1rem;
    }

    .nav-menu {
        flex-direction: column;
        width: 100%;
    }

    .nav-menu li {
        margin: 0;
        width: 100%;
    }

    .nav-menu a {
        display: block;
        width: 100%;
        text-align: center;
    }

    .nav-menu .nav-right {
        margin-left: 0;
        margin-top: 0.5rem;
        flex-direction: column;
        width: 100%;
    }

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

    .form-row {
        grid-template-columns: 1fr;
    }
}

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

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

.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; }

.p-1 { padding: 0.5rem; }
.p-2 { padding: 1rem; }
.p-3 { padding: 1.5rem; }