/* ========== CSS Variables & Theme ========== */
:root {
  --primary: #1e3a8a;
  --primary-dark: #1e3a8a;
  --primary-light: #3b82f6;
  --success: #10b981;
  --success-light: #d1fae5;
  --danger: #ef4444;
  --danger-light: #fee2e2;
  --warning: #f59e0b;
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --border: #475569;
  --radius: 8px;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
}

/* ========== Layout ========== */
.container {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  width: 250px;
  background: var(--bg-secondary);
  padding: 20px;
  border-right: 1px solid var(--border);
  position: fixed;
  height: 100vh;
  overflow-y: auto;
}

.logo {
  margin-bottom: 30px;
}

.logo h1 {
  font-size: 24px;
  font-weight: 700;
  color: var(--primary-light);
}

.nav-menu {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  border-radius: var(--radius);
  color: var(--text-secondary);
  text-decoration: none;
  transition: all 0.3s ease;
  font-size: 14px;
}

.nav-link:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.nav-link.active {
  background: var(--primary);
  color: white;
}

.nav-link .icon {
  font-size: 18px;
}

.main-content {
  margin-left: 250px;
  flex: 1;
  padding: 30px;
}

/* ========== Header ========== */
.top-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 30px;
  flex-wrap: wrap;
  gap: 15px;
}

.top-header h2 {
  font-size: 28px;
  font-weight: 600;
}

.header-actions {
  display: flex;
  gap: 10px;
}

/* ========== Buttons ========== */
.btn-primary,
.btn-secondary,
.btn-icon {
  padding: 10px 20px;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 14px;
  font-weight: 500;
  transition: all 0.3s ease;
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

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

.btn-primary:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
}

.btn-secondary {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--border);
}

.btn-icon {
  padding: 6px 10px;
  background: transparent;
  border: 1px solid var(--border);
}

.btn-icon:hover {
  background: var(--bg-tertiary);
}

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

.btn-icon.danger:hover {
  background: var(--danger-light);
}

/* ========== Dashboard ========== */
.dashboard-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 20px;
}

.stats-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 15px;
  grid-column: 1 / -1;
}

.stat-card {
  background: var(--bg-secondary);
  padding: 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 15px;
  transition: all 0.3s ease;
}

.stat-card:hover {
  border-color: var(--primary-light);
  transform: translateY(-4px);
}

.stat-icon {
  font-size: 32px;
  width: 60px;
  height: 60px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius);
}

.stat-icon.total {
  background: rgba(59, 130, 246, 0.2);
}

.stat-icon.bills {
  background: rgba(16, 185, 129, 0.2);
}

.stat-icon.products {
  background: rgba(249, 115, 22, 0.2);
}

.stat-icon.stock {
  background: rgba(239, 68, 68, 0.2);
}

.stat-info h3 {
  font-size: 14px;
  font-weight: 500;
  color: var(--text-secondary);
  margin-bottom: 5px;
}

.stat-value {
  font-size: 24px;
  font-weight: 700;
  color: var(--primary-light);
}

/* ========== Recent Bills ========== */
.recent-section {
  background: var(--bg-secondary);
  padding: 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  grid-column: 1 / -1;
}

.section-title {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 15px;
}

.bills-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.bill-item {
  background: var(--bg-tertiary);
  padding: 12px 15px;
  border-radius: 6px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.bill-header {
  display: flex;
  gap: 15px;
  flex: 1;
}

.bill-number {
  font-weight: 600;
  color: var(--primary-light);
}

.bill-date {
  color: var(--text-secondary);
  font-size: 12px;
}

.bill-amount {
  font-weight: 600;
  color: var(--success);
}

/* ========== Forms ========== */
.form-container {
  margin-bottom: 30px;
  max-width: 600px;
}

.form-container.hidden {
  display: none;
}

.form-card {
  background: var(--bg-secondary);
  padding: 25px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.form-card h3 {
  margin-bottom: 20px;
  font-size: 18px;
}

.form-group {
  margin-bottom: 15px;
}

.form-group label {
  display: block;
  margin-bottom: 8px;
  font-weight: 500;
  font-size: 14px;
}

.form-group input,
.form-group select {
  width: 100%;
  padding: 10px 12px;
  background: var(--bg-primary);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-primary);
  font-size: 14px;
}

.form-group input:focus,
.form-group select:focus {
  outline: none;
  border-color: var(--primary-light);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 15px;
}

.form-actions {
  display: flex;
  gap: 10px;
  margin-top: 20px;
}

/* ========== Tables ========== */
.table-container {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}

.products-table,
.invoice-table {
  width: 100%;
  border-collapse: collapse;
}

.products-table thead,
.invoice-table thead {
  background: var(--bg-tertiary);
}

.products-table th,
.invoice-table th {
  padding: 15px;
  text-align: left;
  font-weight: 600;
  font-size: 13px;
  color: var(--text-secondary);
  border-bottom: 1px solid var(--border);
}

.products-table td,
.invoice-table td {
  padding: 12px 15px;
  border-bottom: 1px solid var(--border);
}

.products-table tbody tr:hover {
  background: var(--bg-tertiary);
}

.products-table tbody tr.low-stock {
  background: rgba(239, 68, 68, 0.1);
}

.action-buttons {
  display: flex;
  gap: 8px;
}

.empty-state {
  text-align: center;
  padding: 30px;
  color: var(--text-secondary);
  font-style: italic;
}

/* ========== Badges ========== */
.badge {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 600;
}

.badge-success {
  background: var(--success-light);
  color: var(--success);
}

.badge-danger {
  background: var(--danger-light);
  color: var(--danger);
}

/* ========== Billing Page ========== */
.billing-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 25px;
}

.billing-left {
  display: flex;
  flex-direction: column;
  gap: 15px;
}

.invoice-card {
  background: var(--bg-secondary);
  padding: 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.invoice-table {
  margin-bottom: 20px;
  font-size: 13px;
}

.invoice-table td {
  padding: 8px 10px;
}

.invoice-summary {
  background: var(--bg-tertiary);
  padding: 15px;
  border-radius: 6px;
  margin-bottom: 15px;
}

.summary-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 0;
  font-size: 14px;
}

.summary-row.total {
  border-top: 2px solid var(--border);
  padding-top: 12px;
  margin-top: 12px;
  font-size: 16px;
  font-weight: 700;
  color: var(--success);
}

.invoice-actions {
  display: flex;
  gap: 10px;
}

.invoice-actions button {
  flex: 1;
}

/* ========== History Page ========== */
.history-section {
  background: var(--bg-secondary);
  padding: 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.bills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 15px;
}

.bill-card {
  background: var(--bg-tertiary);
  padding: 15px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 12px;
  transition: all 0.3s ease;
}

.bill-card:hover {
  border-color: var(--primary-light);
  transform: translateY(-4px);
}

.bill-card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.bill-card-header h4 {
  font-size: 14px;
  color: var(--primary-light);
}

.bill-date {
  font-size: 12px;
  color: var(--text-secondary);
}

.bill-card-body {
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}

.bill-amount {
  font-size: 20px;
  font-weight: 700;
  color: var(--success);
  margin-bottom: 5px;
}

.bill-card-body small {
  color: var(--text-secondary);
  font-size: 12px;
}

.bill-card-actions {
  display: flex;
  gap: 8px;
}

.bill-card-actions button {
  flex: 1;
  padding: 8px 12px;
  font-size: 12px;
}

/* ========== Modal ========== */
.modal {
  display: none;
  position: fixed;
  z-index: 1000;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.8);
}

.modal-content {
  background: var(--bg-secondary);
  margin: 5% auto;
  padding: 25px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  width: 90%;
  max-width: 800px;
  max-height: 80vh;
  overflow-y: auto;
  position: relative;
}

.close {
  position: absolute;
  right: 15px;
  top: 15px;
  font-size: 28px;
  font-weight: bold;
  color: var(--text-secondary);
  cursor: pointer;
}

.close:hover {
  color: var(--text-primary);
}

.invoice-print {
  padding: 20px;
}

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

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

.invoice-footer {
  margin-top: 25px;
  padding-top: 15px;
  border-top: 1px solid var(--border);
}

/* ========== Responsive ========== */
@media (max-width: 768px) {
  .sidebar {
    width: 100%;
    height: auto;
    position: relative;
    border-right: none;
    border-bottom: 1px solid var(--border);
  }

  .main-content {
    margin-left: 0;
    padding: 20px;
  }

  .nav-menu {
    flex-direction: row;
    flex-wrap: wrap;
  }

  .nav-link {
    flex: 1;
    min-width: 120px;
  }

  .billing-container {
    grid-template-columns: 1fr;
  }

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

  .stats-container {
    grid-template-columns: repeat(2, 1fr);
  }

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

  .modal-content {
    width: 95%;
    margin: 20% auto;
  }

  .bills-grid {
    grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  }

  .table-container {
    overflow-x: auto;
  }
}