:root {
    --gct-primary-grad: linear-gradient(135deg, #2563eb, #1d4ed8);
    --gct-bg-card: #ffffff;
    --gct-text-dark: #1e293b;
    --gct-text-muted: #64748b;
    --gct-border-color: #e2e8f0;
    --gct-input-bg: #f8fafc;
    --gct-accent-error: #ef4444;
    --gct-success: #10b981;
    --gct-radius: 12px;
    --gct-transition: all 0.25s ease-in-out;
}

/* Base Wrapper Scoping */
.gct-calculator-wrapper {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    max-width: 720px;
    margin: 2rem auto;
    color: var(--gct-text-dark);
    line-height: 1.5;
}

/* Card Block Structure */
.gct-card {
    background: var(--gct-bg-card);
    border: 1px solid var(--gct-border-color);
    border-radius: var(--gct-radius);
    padding: 24px;
    margin-bottom: 24px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
    transition: var(--gct-transition);
}

.gct-card:hover {
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.08);
}

/* Headers styling */
.gct-card-header h2, .gct-card-header h3 {
    margin: 0 0 6px 0;
    font-weight: 700;
    font-size: 1.4rem;
    color: var(--gct-text-dark);
    display: flex;
    align-items: center;
    gap: 10px;
}
.gct-card-header h2 i, .gct-card-header h3 i {
    color: #2563eb;
}
.gct-card-header p {
    margin: 0 0 20px 0;
    color: var(--gct-text-muted);
    font-size: 0.95rem;
}

/* Mode Selectors toggle layout */
.gct-mode-selector {
    display: flex;
    background: var(--gct-input-bg);
    padding: 6px;
    border-radius: 8px;
    margin-bottom: 24px;
    border: 1px solid var(--gct-border-color);
}
.gct-mode-btn {
    flex: 1;
    background: transparent;
    border: none;
    padding: 10px;
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    border-radius: 6px;
    color: var(--gct-text-muted);
    transition: var(--gct-transition);
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 8px;
}
.gct-mode-btn.active {
    background: #ffffff;
    color: #2563eb;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

/* Layout System */
.gct-row {
    display: flex;
    gap: 16px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}
.gct-col {
    flex: 1;
    min-width: 200px;
}
.gct-calculator-wrapper label {
    display: block;
    font-weight: 600;
    margin-bottom: 8px;
    font-size: 0.9rem;
    color: var(--gct-text-dark);
}

/* Form controls inputs */
.gct-input-group {
    display: flex;
    align-items: center;
    background: var(--gct-input-bg);
    border: 1px solid var(--gct-border-color);
    border-radius: 8px;
    overflow: hidden;
    transition: var(--gct-transition);
}
.gct-input-group:focus-within {
    border-color: #2563eb;
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}
.gct-input-addon {
    background: var(--gct-border-color);
    padding: 12px 16px;
    font-weight: 600;
    color: var(--gct-text-muted);
    font-size: 0.95rem;
}
.gct-input-group input[type="number"], 
.gct-input-group input[type="text"],
.gct-calculator-wrapper select {
    width: 100%;
    border: none !important;
    background: transparent !important;
    padding: 12px;
    outline: none !important;
    font-size: 1rem;
    color: var(--gct-text-dark);
    margin: 0 !important;
    box-shadow: none !important;
}
.gct-calculator-wrapper select {
    background: var(--gct-input-bg) !important;
    border: 1px solid var(--gct-border-color) !important;
    border-radius: 8px;
    cursor: pointer;
}

/* Predefined tax target rates block matrix */
.gct-rates-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(75px, 1fr));
    gap: 10px;
}
.gct-rate-btn {
    background: #ffffff;
    border: 1px solid var(--gct-border-color);
    padding: 12px 8px;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer;
    text-align: center;
    transition: var(--gct-transition);
}
.gct-rate-btn:hover {
    border-color: #2563eb;
    background: var(--gct-input-bg);
}
.gct-rate-btn.active {
    background: var(--gct-primary-grad);
    color: #ffffff;
    border-color: transparent;
}

/* Error Element styling */
.gct-error-message {
    background: #fef2f2;
    border-left: 4px solid var(--gct-accent-error);
    color: #991b1b;
    padding: 12px 16px;
    border-radius: 6px;
    font-size: 0.9rem;
    margin-bottom: 20px;
    font-weight: 500;
}

/* Form execution utility layouts */
.gct-form-actions {
    display: flex;
    justify-content: flex-end;
}
.gct-btn-secondary {
    background: #f1f5f9;
    color: #475569;
    border: 1px solid var(--gct-border-color);
    padding: 10px 20px;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer;
    transition: var(--gct-transition);
}
.gct-btn-secondary:hover {
    background: #e2e8f0;
    color: #1e293b;
}

/* Invoice Module Template representation */
.gct-invoice-box {
    border: 2px dashed var(--gct-border-color);
    border-radius: 8px;
    padding: 20px;
    background: #fafafa;
    margin-bottom: 20px;
}
.gct-invoice-row {
    display: flex;
    justify-content: space-between;
    padding: 12px 0;
    border-bottom: 1px solid var(--gct-border-color);
    font-size: 0.95rem;
}
.gct-invoice-row.header-row {
    font-weight: 700;
    text-transform: uppercase;
    font-size: 0.85rem;
    letter-spacing: 0.5px;
    color: var(--gct-text-muted);
    border-bottom: 2px solid var(--gct-border-color);
}
.gct-invoice-row.total-row {
    border-bottom: none;
    padding-top: 16px;
    font-weight: 700;
    font-size: 1.2rem;
    color: #2563eb;
}

/* Utility Toolbars Layout */
.gct-output-utilities {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
}
.gct-util-btn {
    flex: 1;
    min-width: 120px;
    background: #ffffff;
    border: 1px solid var(--gct-border-color);
    padding: 10px 14px;
    border-radius: 8px;
    font-weight: 600;
    font-size: 0.9rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    transition: var(--gct-transition);
    color: var(--gct-text-dark);
}
.gct-util-btn:hover {
    border-color: #2563eb;
    color: #2563eb;
    background: var(--gct-input-bg);
}

/* History Responsive Tables Data viewports style */
.gct-responsive-table {
    overflow-x: auto;
}
.gct-history-table {
    width: 100%;
    border-collapse: collapse;
    text-align: left;
    font-size: 0.9rem;
}
.gct-history-table th, .gct-history-table td {
    padding: 12px;
    border-bottom: 1px solid var(--gct-border-color);
}
.gct-history-table th {
    background: var(--gct-input-bg);
    color: var(--gct-text-muted);
    font-weight: 600;
}
.gct-history-tag {
    display: inline-block;
    padding: 2px 6px;
    border-radius: 4px;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
}
.gct-history-tag.add { background: #dcfce7; color: #166534; }
.gct-history-tag.remove { background: #fee2e2; color: #991b1b; }

/* Formulas Section Info styling */
.gct-formula-body {
    display: flex;
    flex-direction: column;
    gap: 16px;
}
.gct-formula-block h4 {
    margin: 0 0 6px 0;
    font-size: 0.95rem;
    color: var(--gct-text-dark);
}
.gct-formula-block p {
    margin: 4px 0;
}
.gct-formula-block code {
    display: block;
    background: var(--gct-input-bg);
    padding: 8px 12px;
    border-radius: 6px;
    font-size: 0.88rem;
    color: #0f172a;
    border: 1px solid var(--gct-border-color);
}

/* Dark Mode Ecosystem support fallback rules styling */
@media (prefers-color-scheme: dark) {
    .gct-card:not(.gct-results-section) {
        --gct-bg-card: #1e293b;
        --gct-text-dark: #f8fafc;
        --gct-text-muted: #94a3b8;
        --gct-border-color: #334155;
        --gct-input-bg: #0f172a;
    }
    .gct-invoice-box {
        background: #0f172a !important;
    }
    .gct-mode-btn.active {
        background: #334155 !important;
        color: #38bdf8 !important;
    }
    .gct-rate-btn {
        background: #1e293b;
        color: #f8fafc;
    }
    .gct-rate-btn.active {
        background: var(--gct-primary-grad);
        color: #ffffff;
    }
    .gct-btn-secondary {
        background: #334155;
        color: #f8fafc;
    }
    .gct-btn-secondary:hover {
        background: #475569;
    }
    .gct-util-btn {
        background: #1e293b;
        color: #f8fafc;
    }
    .gct-formula-block code {
        color: #38bdf8;
    }
}

/* Printing Optimization Style Blocks overrides definitions */
@media print {
    body * {
        visibility: hidden;
    }
    #gct-printable-invoice, #gct-printable-invoice * {
        visibility: visible;
    }
    #gct-printable-invoice {
        position: absolute;
        left: 0;
        top: 0;
        width: 100%;
        border: 1px solid #000;
        padding: 30px;
    }
}