:root {
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --primary-light: #eff6ff;
    --success: #16a34a;
    --danger: #dc2626;
    --warning: #d97706;
    --gray-50: #f9fafb;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-500: #6b7280;
    --gray-700: #374151;
    --gray-900: #111827;
    --shadow: 0 1px 3px rgba(0,0,0,.1), 0 1px 2px rgba(0,0,0,.06);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,.1), 0 2px 4px -1px rgba(0,0,0,.06);
    --radius: 8px;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--gray-50);
    color: var(--gray-900);
    line-height: 1.5;
    font-size: 14px;
}

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Layout */
.navbar {
    background: #fff;
    border-bottom: 1px solid var(--gray-200);
    padding: 0 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 56px;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}
.navbar-brand {
    font-size: 18px;
    font-weight: 700;
    color: var(--primary);
    text-decoration: none;
}
.navbar-nav {
    display: flex;
    align-items: center;
    gap: 8px;
}
.nav-link {
    padding: 6px 12px;
    border-radius: 6px;
    color: var(--gray-700);
    font-weight: 500;
    text-decoration: none;
    transition: background .15s;
}
.nav-link:hover { background: var(--gray-100); text-decoration: none; }
.nav-link.active { background: var(--primary-light); color: var(--primary); }

.container { max-width: 1100px; margin: 0 auto; padding: 32px 24px; }
.container-sm { max-width: 480px; margin: 0 auto; padding: 32px 24px; }

/* Cards */
.card {
    background: #fff;
    border-radius: var(--radius);
    border: 1px solid var(--gray-200);
    box-shadow: var(--shadow);
}
.card-header {
    padding: 16px 20px;
    border-bottom: 1px solid var(--gray-200);
    display: flex;
    align-items: center;
    justify-content: space-between;
}
.card-title { font-size: 16px; font-weight: 600; }
.card-body { padding: 20px; }

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 8px 16px;
    border-radius: 6px;
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    border: 1px solid transparent;
    text-decoration: none;
    transition: all .15s;
    white-space: nowrap;
}
.btn:hover { text-decoration: none; }
.btn-primary { background: var(--primary); color: #fff; border-color: var(--primary); }
.btn-primary:hover { background: var(--primary-dark); }
.btn-secondary { background: #fff; color: var(--gray-700); border-color: var(--gray-300); }
.btn-secondary:hover { background: var(--gray-50); }
.btn-success { background: var(--success); color: #fff; border-color: var(--success); }
.btn-danger { background: var(--danger); color: #fff; border-color: var(--danger); }
.btn-sm { padding: 4px 10px; font-size: 12px; }
.btn-icon { padding: 6px 8px; }

/* Forms */
.form-group { margin-bottom: 16px; }
.form-label { display: block; font-weight: 500; margin-bottom: 6px; color: var(--gray-700); }
.form-control {
    width: 100%;
    padding: 8px 12px;
    border: 1px solid var(--gray-300);
    border-radius: 6px;
    font-size: 14px;
    color: var(--gray-900);
    background: #fff;
    transition: border-color .15s, box-shadow .15s;
}
.form-control:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37,99,235,.1);
}
select.form-control { cursor: pointer; }
textarea.form-control { resize: vertical; min-height: 80px; }

/* Grid */
.grid { display: grid; gap: 16px; }
.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

/* Table */
.table-wrap { overflow-x: auto; }
table { width: 100%; border-collapse: collapse; }
th {
    background: var(--gray-50);
    border-bottom: 2px solid var(--gray-200);
    padding: 10px 12px;
    text-align: left;
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: .05em;
    color: var(--gray-500);
    white-space: nowrap;
}
td {
    padding: 12px 12px;
    border-bottom: 1px solid var(--gray-100);
    vertical-align: middle;
}
tr:last-child td { border-bottom: none; }
tr:hover td { background: var(--gray-50); }

/* Badges */
.badge {
    display: inline-block;
    padding: 2px 8px;
    border-radius: 99px;
    font-size: 11px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: .05em;
}
.badge-draft { background: var(--gray-100); color: var(--gray-700); }
.badge-sent { background: #dbeafe; color: #1d4ed8; }
.badge-paid { background: #dcfce7; color: #15803d; }
.badge-overdue { background: #fee2e2; color: #b91c1c; }

/* Alerts */
.alert {
    padding: 12px 16px;
    border-radius: var(--radius);
    margin-bottom: 20px;
    font-size: 14px;
    display: flex;
    align-items: center;
    gap: 8px;
}
.alert-success { background: #dcfce7; color: #15803d; border: 1px solid #bbf7d0; }
.alert-error   { background: #fee2e2; color: #b91c1c; border: 1px solid #fecaca; }
.alert-info    { background: #dbeafe; color: #1d4ed8; border: 1px solid #bfdbfe; }

/* Stats */
.stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: 16px; margin-bottom: 24px; }
.stat-card {
    background: #fff;
    border: 1px solid var(--gray-200);
    border-radius: var(--radius);
    padding: 20px;
    box-shadow: var(--shadow);
}
.stat-label { font-size: 12px; color: var(--gray-500); text-transform: uppercase; letter-spacing: .05em; margin-bottom: 8px; }
.stat-value { font-size: 28px; font-weight: 700; color: var(--gray-900); }
.stat-sub { font-size: 12px; color: var(--gray-500); margin-top: 4px; }

/* Login */
.login-wrap {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--primary) 0%, #1e40af 100%);
    padding: 24px;
}
.login-card {
    background: #fff;
    border-radius: 12px;
    padding: 40px;
    width: 100%;
    max-width: 420px;
    box-shadow: 0 20px 60px rgba(0,0,0,.2);
}
.login-logo { text-align: center; margin-bottom: 32px; }
.login-logo h1 { font-size: 24px; font-weight: 800; color: var(--primary); }
.login-logo p { color: var(--gray-500); font-size: 14px; margin-top: 4px; }

/* Invoice items table */
.items-table th, .items-table td { padding: 8px 10px; }
.items-table input { background: transparent; border: none; padding: 4px; width: 100%; }
.items-table input:focus { outline: 1px solid var(--primary); border-radius: 4px; background: #fff; }
.items-table .btn-remove { color: var(--danger); }

/* Totals */
.totals-box { max-width: 320px; margin-left: auto; margin-top: 16px; }
.totals-row { display: flex; justify-content: space-between; padding: 6px 0; font-size: 14px; }
.totals-row.total { font-weight: 700; font-size: 16px; border-top: 2px solid var(--gray-900); padding-top: 10px; margin-top: 4px; }

/* Flex utilities */
.flex { display: flex; }
.flex-between { display: flex; justify-content: space-between; align-items: center; }
.flex-end { display: flex; justify-content: flex-end; }
.gap-2 { gap: 8px; }
.gap-3 { gap: 12px; }
.mt-1 { margin-top: 4px; }
.mt-2 { margin-top: 8px; }
.mt-3 { margin-top: 12px; }
.mt-4 { margin-top: 16px; }
.mt-6 { margin-top: 24px; }
.mb-4 { margin-bottom: 16px; }
.text-muted { color: var(--gray-500); }
.text-right { text-align: right; }
.text-sm { font-size: 12px; }
.font-bold { font-weight: 700; }
.w-full { width: 100%; }

/* Responsive */
@media (max-width: 768px) {
    .stats { grid-template-columns: repeat(2, 1fr); }
    .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
    .navbar { padding: 0 16px; }
    .container { padding: 16px; }
}
@media (max-width: 480px) {
    .stats { grid-template-columns: 1fr; }
    .login-card { padding: 24px; }
}