:root {
  /* Colors - Blue Gradient Theme */
  --color-primary-dark: rgba(29, 78, 216, 1);
  --color-primary: rgba(59, 130, 246, 1);
  --color-primary-light: rgba(96, 165, 250, 1);
  --color-primary-hover: rgba(37, 99, 235, 1);
  --color-primary-active: var(--color-primary-dark);
  
  --color-background: rgba(243, 244, 246, 1); /* Gray-100 */
  --color-surface: rgba(255, 255, 255, 1); /* White */
  --color-text: rgba(17, 24, 39, 1); /* Gray-900 */
  --color-text-secondary: rgba(107, 114, 128, 1); /* Gray-500 */
  --color-btn-primary-text: rgba(255, 255, 255, 1);
  
  --color-border: rgba(229, 231, 235, 1); /* Gray-200 */
  --color-card-border: var(--color-border);
  --color-card-border-inner: var(--color-border);

  --color-error: rgba(239, 68, 68, 1);
  --color-success: rgba(16, 185, 129, 1);
  --color-warning: rgba(245, 158, 11, 1);
  --color-info: rgba(59, 130, 246, 1);
  --color-focus-ring: rgba(59, 130, 246, 0.4);

  /* Gradients */
  --gradient-primary: linear-gradient(135deg, var(--color-primary-light) 0%, var(--color-primary) 100%);
  --gradient-primary-hover: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-hover) 100%);
  --gradient-surface: linear-gradient(135deg, #f5f8ff 0%, #eef4ff 100%);
  --gradient-header: linear-gradient(135deg, #E0F7FA 0%, #B3E5FC 100%);
  --gradient-report-header: linear-gradient(135deg, #e3f2fd 0%, #bbdefb 100%);
  --gradient-report-total: linear-gradient(135deg, #e3f2fd 0%, #bbdefb 100%);
  
  /* RGB versions for opacity control */
  --color-primary-rgb: 59, 130, 246;
  --color-success-rgb: 16, 185, 129;
  --color-error-rgb: 239, 68, 68;
  --color-warning-rgb: 245, 158, 11;
  --color-info-rgb: var(--color-primary-rgb);
  
  /* Typography */
  --font-family-base: "Inter", "Helvetica Neue", "Helvetica", "Arial", "PingFang TC", "Hiragino Sans GB", "Microsoft JhengHei", "WenQuanYi Micro Hei", sans-serif;
  --font-size-sm: 12px;
  --font-size-base: 14px;
  --font-size-lg: 16px;
  --font-size-xl: 18px;
  --font-size-2xl: 20px;
  --font-size-3xl: 24px;
  
  /* Spacing */
  --space-4: 4px;
  --space-8: 8px;
  --space-12: 12px;
  --space-16: 16px;
  --space-20: 20px;
  --space-24: 24px;
  --space-32: 32px;
  
  /* Border Radius */
  --radius-sm: 4px;
  --radius-base: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-full: 9999px;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);

  /* Layout */
  --sidebar-width: 220px;
  --bottom-nav-height: 60px;
  --mobile-header-height: 56px;
}

/* Base styles */
html {
  font-family: var(--font-family-base);
  background-color: var(--color-background);
  color: var(--color-text);
}
body, #app { margin: 0; padding: 0; }
*, *::before, *::after { box-sizing: border-box; }

/* Typography */
h1, h2, h3, h4, h5, h6 { margin: 0; font-weight: 600; }
h1.section-title { font-size: var(--font-size-3xl); margin-bottom: var(--space-24); }

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-8);
  padding: var(--space-8) var(--space-16);
  border-radius: var(--radius-base);
  font-size: var(--font-size-base);
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease-in-out;
  border: 1px solid transparent;
  text-decoration: none;
}
.btn:focus-visible { outline: 2px solid var(--color-focus-ring); }
.btn--primary {
  background: var(--gradient-primary);
  color: var(--color-btn-primary-text);
  border-color: var(--color-primary);
  box-shadow: var(--shadow-sm);
}
.btn--primary:hover {
    background: var(--gradient-primary-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}
.btn--secondary { background: var(--color-surface); color: var(--color-text); border-color: var(--color-border); }
.btn--secondary:hover { background-color: rgba(var(--color-primary-rgb), 0.05); border-color: var(--color-primary-light); }
.btn--outline { background: transparent; border: 1px solid var(--color-border); color: var(--color-text); }
.btn--outline:hover { background: rgba(var(--color-primary-rgb), 0.05); }
.btn--sm { padding: var(--space-4) var(--space-12); font-size: var(--font-size-sm); }
.btn--full-width { width: 100%; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }
.btn i { width: 16px; height: 16px; }

/* Forms */
.form-control {
  display: block;
  width: 100%;
  padding: var(--space-8) var(--space-12);
  font-size: var(--font-size-base);
  color: var(--color-text);
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-base);
  transition: border-color 0.2s, box-shadow 0.2s;
}
.form-control:focus { border-color: var(--color-primary); box-shadow: 0 0 0 2px var(--color-focus-ring); outline: none; }
.form-label { display: block; margin-bottom: var(--space-8); font-weight: 500; }
.form-group { margin-bottom: var(--space-16); }

/* Card */
.card {
  background-color: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-card-border);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}
.card__body { padding: var(--space-16); }

/* Status Badge */
.status-badge {
    display: inline-flex;
    align-items: center;
    padding: var(--space-4) var(--space-12);
    border-radius: var(--radius-full);
    font-weight: 500;
    font-size: var(--font-size-sm);
    --status-bg-opacity: 0.1;
    --status-border-opacity: 0.2;
}
.status-badge--draft {
    background-color: rgba(var(--color-text-secondary-rgb, 107, 114, 128), var(--status-bg-opacity));
    color: var(--color-text-secondary);
}
.status-badge--confirmed {
    background-color: rgba(var(--color-primary-rgb), var(--status-bg-opacity));
    color: var(--color-primary);
}

/* Layout */
#app { display: flex; }
.main {
    flex-grow: 1;
    padding: var(--space-24);
    padding-top: calc(var(--mobile-header-height) + var(--space-24)); /* Space for mobile header */
    padding-bottom: calc(var(--bottom-nav-height) + var(--space-24)); /* Space for bottom nav */
}
.section { display: none; }
.section.active { display: block; }
.section-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: var(--space-16); }

/* Navigation */
.mobile-header {
    display: none; /* Hidden by default */
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: var(--mobile-header-height);
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    justify-content: center;
    align-items: center;
    z-index: 900;
    box-shadow: var(--shadow-sm);
}
.mobile-header h2 { font-size: var(--font-size-lg); color: var(--color-text); }

.sidebar {
    position: fixed;
    z-index: 1000;
    display: flex;
}
.sidebar .nav-btn {
    display: flex;
    align-items: center;
    width: 100%;
    padding: var(--space-12) var(--space-16);
    gap: var(--space-12);
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    font-size: var(--font-size-base);
    border-radius: var(--radius-base);
    transition: background-color 0.2s, color 0.2s;
    cursor: pointer;
}
.sidebar .nav-btn:hover { background-color: rgba(var(--color-primary-rgb), 0.1); color: var(--color-primary); }
.sidebar .nav-btn.active {
    background: var(--gradient-primary);
    color: white;
    font-weight: 600;
    box-shadow: var(--shadow-md);
}
.sidebar .nav-btn i { width: 20px; height: 20px; }

/* Dashboard */
.stats-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: var(--space-16); margin-bottom: var(--space-24); }
.stat-card { background: var(--gradient-surface); padding: var(--space-20); border-radius: var(--radius-md); text-align: center; border: 1px solid var(--color-border); }
.stat-card h3 { color: var(--color-text-secondary); font-size: var(--font-size-sm); margin-bottom: var(--space-8); }
.stat-number { font-size: var(--font-size-3xl); font-weight: 700; color: var(--color-primary); }
.quick-actions .action-buttons { display: flex; flex-wrap: wrap; gap: var(--space-12); }

/* Tables */
.table-responsive { overflow-x: auto; }
.data-table { width: 100%; border-collapse: collapse; white-space: nowrap; }
.data-table th, .data-table td { padding: var(--space-12); text-align: left; border-bottom: 1px solid var(--color-border); }
.data-table th { background: rgba(var(--color-primary-rgb), 0.05); font-weight: 600; font-size: var(--font-size-sm); text-transform: uppercase; }
.data-table tr:hover { background: rgba(var(--color-primary-rgb), 0.02); }
.data-table .actions { display: flex; gap: var(--space-8); flex-wrap: nowrap; }

/* Document Tabs */
.document-tabs { display: flex; flex-wrap: wrap; gap: var(--space-8); margin-bottom: var(--space-16); }
.tab-btn { padding: var(--space-8) var(--space-16); border: 1px solid var(--color-border); background: var(--color-surface); color: var(--color-text); border-radius: var(--radius-base); cursor: pointer; transition: all 0.2s; }
.tab-btn.active { background: var(--color-primary); color: white; border-color: var(--color-primary); }

/* Modal */
.modal { position: fixed; top: 0; left: 0; width: 100%; height: 100%; background: rgba(0, 0, 0, 0.5); display: flex; align-items: center; justify-content: center; z-index: 1100; padding: var(--space-16); }
.modal.hidden { display: none; }
.modal-content { background: var(--color-surface); border-radius: var(--radius-lg); box-shadow: var(--shadow-lg); width: 100%; max-width: 800px; max-height: 90vh; display: flex; flex-direction: column; }
.modal-header { display: flex; justify-content: space-between; align-items: center; padding: var(--space-16); border-bottom: 1px solid var(--color-border); background: var(--gradient-header); }
.modal-header h3 { font-size: var(--font-size-lg); }
.modal-close { background: none; border: none; font-size: var(--font-size-2xl); cursor: pointer; color: var(--color-text-secondary); }
.modal-body { padding: var(--space-20); overflow-y: auto; }

/* Document Form */
.document-header { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: var(--space-16); padding: var(--space-16); background: var(--gradient-surface); border-radius: var(--radius-base); margin-bottom: var(--space-16); }
.items-header { background: rgba(var(--color-primary-rgb), 0.05); padding: var(--space-12); font-weight: 600; display: grid; grid-template-columns: 2fr 1fr 1fr 1fr auto; gap: var(--space-12); }
.item-row { padding: var(--space-8); border-bottom: 1px solid var(--color-border); display: grid; grid-template-columns: 2fr 1fr 1fr 1fr auto; gap: var(--space-12); align-items: center; }
.document-total { background: var(--gradient-surface); padding: var(--space-16); border-radius: var(--radius-base); border: 1px solid var(--color-primary-light); margin-top: var(--space-16); }
.total-row { display: flex; justify-content: space-between; padding: var(--space-4) 0; }
.final-total-row { font-weight: bold; font-size: var(--font-size-lg); color: var(--color-primary); border-top: 1px solid var(--color-primary-light); margin-top: var(--space-8); padding-top: var(--space-8); }

/* Conversion & Message Modals */
.conversion-confirm, .conversion-success, .message-modal, .confirm-dialog { padding: var(--space-16); text-align: center; }
.conversion-info, .success-info { background: var(--gradient-surface); padding: var(--space-16); border-radius: var(--radius-base); border: 1px solid var(--color-border); margin-bottom: var(--space-16); text-align: left; }
.conversion-actions, .success-actions, .message-actions, .confirm-actions { display: flex; gap: var(--space-12); justify-content: center; margin-top: var(--space-16); }

/* Report Styles */
.print-report { padding: var(--space-24); }
.report-header { display: flex; justify-content: space-between; gap: var(--space-24); margin-bottom: var(--space-24); padding-bottom: var(--space-16); border-bottom: 2px solid var(--color-primary); }
.company-info, .document-info { padding: var(--space-16); border-radius: var(--radius-base); }
.company-info { background: var(--gradient-report-header); border: 1px solid var(--color-primary-light); }
.company-info h2 { color: var(--color-primary-dark); }
.document-info { background: var(--gradient-surface); }
.document-info h3 { color: var(--color-primary); }
.print-report table { width: 100%; border-collapse: collapse; font-size: 12px; }
.print-report th { background: var(--gradient-report-header); padding: 8px; text-align: left; font-weight: 600; }
.print-report td { padding: 8px; border-bottom: 1px solid var(--color-border); }
.print-report .report-totals { background: var(--gradient-report-total); padding: var(--space-16); border-radius: var(--radius-base); border: 1px solid var(--color-primary); margin-top: var(--space-20); }
.print-report .report-totals .total-row { display: flex; justify-content: space-between; padding: 2px 0; }
.print-report .report-totals .final-total-row { font-size: 1.2em; font-weight: bold; color: var(--color-primary-dark); padding-top: 8px; border-top: 1px solid var(--color-primary); }

/* Responsive Design: Mobile First */

/* Mobile (default styles) */
.sidebar {
    bottom: 0;
    left: 0;
    right: 0;
    height: var(--bottom-nav-height);
    flex-direction: row;
    background: var(--color-surface);
    border-top: 1px solid var(--color-border);
    box-shadow: 0 -2px 5px rgba(0,0,0,0.05);
}
.sidebar .sidebar-header { display: none; }
.sidebar .nav-links { display: flex; justify-content: space-around; width: 100%; }
.sidebar .nav-btn { flex-direction: column; justify-content: center; padding: var(--space-4) 0; height: 100%; border-radius: 0; font-size: 10px; }
.sidebar .nav-btn span { margin-top: var(--space-4); }
.sidebar .nav-btn.active { background: transparent; color: var(--color-primary); }
.sidebar .nav-btn.active::before {
    content: '';
    position: absolute;
    top: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 40px;
    height: 3px;
    background-color: var(--color-primary);
    border-radius: 2px;
}
.mobile-header { display: flex; }
.main { padding-left: var(--space-16); padding-right: var(--space-16); }
.action-buttons { flex-direction: column; }
.action-buttons .btn { width: 100%; }
.data-table .actions { flex-wrap: wrap; }


/* Tablet and Desktop (large screens) */
@media (min-width: 768px) {
    #app { flex-direction: row; }
    .mobile-header { display: none; }
    .main {
        margin-left: var(--sidebar-width);
        padding: var(--space-32);
        padding-top: var(--space-32); /* Reset padding */
        padding-bottom: var(--space-32);
    }
    .sidebar {
        top: 0;
        bottom: 0;
        left: 0;
        width: var(--sidebar-width);
        height: 100vh;
        flex-direction: column;
        background: var(--color-surface);
        padding: var(--space-16);
        border-right: 1px solid var(--color-border);
        box-shadow: none;
    }
    .sidebar .sidebar-header { display: block; padding: var(--space-16) 0; margin-bottom: var(--space-16); }
    .sidebar .sidebar-header h2 { color: var(--color-primary); text-align: center; }
    .sidebar .nav-links { flex-direction: column; gap: var(--space-8); }
    .sidebar .nav-btn {
        flex-direction: row;
        justify-content: flex-start;
        height: auto;
        font-size: var(--font-size-base);
        border-radius: var(--radius-base);
    }
    .sidebar .nav-btn span { margin-top: 0; }
    .sidebar .nav-btn.active {
        background: var(--gradient-primary); /* Re-apply gradient for desktop */
        color: white;
    }
    .sidebar .nav-btn.active::before { display: none; }
    .action-buttons { flex-direction: row; }
    .action-buttons .btn { width: auto; }
}