:root {
    /* Color Palette - Premium & Trustworthy */
    --primary-color: #2563EB;
    /* Royal Blue */
    --primary-hover: #1D4ED8;
    --secondary-color: #1E293B;
    /* Slate 800 */
    --accent-color: #10B981;
    /* Emerald Green */
    --danger-color: #EF4444;
    /* Red 500 */
    --text-main: #111827;
    /* Gray 900 */
    --text-muted: #6B7280;
    /* Gray 500 */
    --bg-body: #F9FAFB;
    /* Gray 50 */
    --bg-card: #FFFFFF;
    --border-color: #E5E7EB;
    /* Gray 200 */

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 4rem;

    /* 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 -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

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

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    color: var(--text-main);
    background-color: var(--bg-body);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

h1,
h2,
h3,
h4 {
    color: var(--secondary-color);
    line-height: 1.2;
    margin-bottom: var(--spacing-sm);
}

p {
    margin-bottom: var(--spacing-md);
    color: var(--text-muted);
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.2s;
}

a:hover {
    color: var(--primary-hover);
}

.container {
    max-width: 1024px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* Header */
.site-header {
    background: var(--bg-card);
    border-bottom: 1px solid var(--border-color);
    padding: var(--spacing-sm) 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

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

.logo {
    display: flex;
    align-items: center;
    gap: 8px;
    font-weight: 700;
    font-size: 1.25rem;
    color: var(--secondary-color);
}

.main-nav {
    display: flex;
    gap: var(--spacing-md);
}

.main-nav a {
    color: var(--text-muted);
    font-weight: 500;
}

.main-nav a:hover {
    color: var(--primary-color);
}

/* Hero Section */
.hero-section {
    padding: var(--spacing-xl) 0;
    text-align: center;
}

.hero-section h1 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: var(--spacing-xs);
    letter-spacing: -0.02em;
}

.hero-section .subtitle {
    font-size: 1.25rem;
    max-width: 600px;
    margin: 0 auto var(--spacing-lg);
}

/* Calculator Card */
/* Calculator Grid Layout */
.calculator-card {
    background: var(--bg-card);
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    padding: var(--spacing-lg);
    max-width: 1100px;
    /* Increased width for side-by-side */
    margin: 0 auto;
    border: 1px solid var(--border-color);
    text-align: left;
}

.calculator-grid {
    display: grid;
    grid-template-columns: 1fr 340px;
    /* Main tool takes remaining space, calc fixed width */
    gap: var(--spacing-lg);
    align-items: start;
}

.sum-tool {
    min-width: 0;
    /* Prevents grid blowout */
}

/* Basic Calculator Styles */
.basic-calc-container {
    background: var(--bg-body);
    padding: var(--spacing-md);
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

.basic-calc-container h3 {
    font-size: 1rem;
    margin-bottom: var(--spacing-sm);
    text-align: center;
    color: var(--text-muted);
}

.basic-calc {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.calc-display {
    background: #fff;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 12px;
    text-align: right;
    margin-bottom: 4px;
}

.calc-history {
    font-size: 0.75rem;
    color: var(--text-muted);
    height: 1.2em;
    overflow: hidden;
}

.calc-screen {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--secondary-color);
    word-break: break-all;
}

.calc-keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 8px;
}

.calc-keys button {
    padding: 12px;
    font-size: 1.125rem;
    border: 1px solid var(--border-color);
    background: white;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.1s;
    font-weight: 500;
    color: var(--text-main);
}

.calc-keys button:hover {
    background: var(--bg-body);
    border-color: var(--primary-color);
}

.calc-keys button:active {
    transform: scale(0.98);
}

.key-op {
    background: #EFF6FF !important;
    /* Blue 50 */
    color: var(--primary-color) !important;
    font-weight: 700 !important;
}

.key-equal {
    grid-column: span 1;
    grid-row: span 2;
    background: var(--primary-color) !important;
    color: white !important;
    border-color: var(--primary-color) !important;
}

.key-equal:hover {
    background: var(--primary-hover) !important;
}

.key-zero {
    grid-column: span 2;
}

.btn-insert {
    width: 100%;
    margin-top: 8px;
    padding: 8px;
    background: var(--accent-color);
    color: white;
    border: none;
    border-radius: 6px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    transition: background 0.2s;
}

.btn-insert:hover {
    background: #059669;
    /* Emerald 600 */
}

/* Responsive adjustments */
@media (max-width: 900px) {
    .calculator-grid {
        grid-template-columns: 1fr;
        /* Stack vertically */
    }

    .basic-calc-container {
        max-width: 400px;
        margin: 0 auto;
        width: 100%;
    }
}

.input-group label {
    display: block;
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
    color: var(--secondary-color);
}

.input-wrapper {
    position: relative;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    transition: border-color 0.2s;
    background: #fff;
}

.input-wrapper:focus-within {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

textarea {
    width: 100%;
    height: 180px;
    border: none;
    padding: var(--spacing-sm);
    font-family: monospace;
    font-size: 1rem;
    resize: vertical;
    outline: none;
    border-radius: 8px;
    background: transparent;
}

.input-actions {
    position: absolute;
    bottom: 8px;
    right: 8px;
    display: flex;
    gap: 8px;
}

.btn-text {
    background: rgba(255, 255, 255, 0.9);
    border: 1px solid var(--border-color);
    padding: 4px 12px;
    border-radius: 6px;
    font-size: 0.875rem;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.2s;
}

.btn-text:hover {
    background: var(--bg-body);
}

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

.btn-text.text-danger:hover {
    background: rgba(239, 68, 68, 0.1);
}

.input-hint {
    font-size: 0.875rem;
    margin-top: 6px;
    color: var(--text-muted);
}

.action-bar {
    margin-top: var(--spacing-lg);
    display: flex;
    justify-content: center;
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 0.75rem 2rem;
    border-radius: 8px;
    font-weight: 600;
    border: none;
    cursor: pointer;
    font-size: 1rem;
    transition: transform 0.1s, box-shadow 0.2s;
}

.btn-primary {
    background: var(--primary-color);
    color: white;
    box-shadow: 0 4px 6px rgba(37, 99, 235, 0.25);
}

.btn-primary:hover {
    background: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: 0 6px 8px rgba(37, 99, 235, 0.3);
}

.btn-primary:active {
    transform: translateY(0);
}

/* Results Area */
.results-area {
    margin-top: var(--spacing-lg);
    padding-top: var(--spacing-lg);
    border-top: 1px solid var(--border-color);
    animation: slideDown 0.3s ease-out;
}

.hidden {
    display: none;
}

@keyframes slideDown {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.result-card {
    background: var(--bg-body);
    border-radius: 8px;
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    border: 1px solid var(--border-color);
}

.primary-result {
    background: #EFF6FF;
    /* Blue 50 */
    border-color: #DBEAFE;
    /* Blue 200 */
    text-align: center;
}

.primary-result .label {
    display: block;
    font-size: 0.875rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--primary-color);
    font-weight: 700;
    margin-bottom: 4px;
}

.primary-result .value-wrapper {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
}

.primary-result .value {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--secondary-color);
}

.btn-icon {
    background: white;
    border: 1px solid var(--border-color);
    width: 36px;
    height: 36px;
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    color: var(--text-muted);
    transition: all 0.2s;
}

.btn-icon:hover {
    color: var(--primary-color);
    border-color: var(--primary-color);
}

.secondary-results {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: var(--spacing-sm);
}

.secondary-results .result-card {
    margin-bottom: 0;
    text-align: center;
    padding: var(--spacing-sm);
}

.secondary-results .label {
    display: block;
    font-size: 0.75rem;
    text-transform: uppercase;
    color: var(--text-muted);
    font-weight: 600;
    margin-bottom: 4px;
}

.secondary-results .value-small {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--secondary-color);
}

/* Content Sections */
.content-section {
    padding: var(--spacing-xl) 0;
}

.bg-light {
    background: #fff;
    border-top: 1px solid var(--border-color);
    border-bottom: 1px solid var(--border-color);
}

.text-block {
    max-width: 720px;
    margin: 0 auto;
}

.text-block h2 {
    font-size: 2rem;
    margin-bottom: var(--spacing-md);
}

.steps-list {
    counter-reset: steps;
    list-style: none;
}

.steps-list li {
    position: relative;
    padding-left: 3rem;
    margin-bottom: var(--spacing-md);
}

.steps-list li::before {
    counter-increment: steps;
    content: counter(steps);
    position: absolute;
    left: 0;
    top: 0;
    width: 2rem;
    height: 2rem;
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
}

/* FAQ Grid */
.faq-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.faq-item h3 {
    font-size: 1.125rem;
    margin-bottom: 8px;
    color: var(--text-main);
}

/* Footer */
.site-footer {
    padding: var(--spacing-lg) 0;
    background: var(--bg-card);
    border-top: 1px solid var(--border-color);
    margin-top: auto;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-md);
}

.footer-brand span {
    font-weight: 700;
    color: var(--secondary-color);
}

.footer-brand p {
    font-size: 0.875rem;
    margin: 0;
}

.footer-links {
    display: flex;
    gap: var(--spacing-md);
}

.footer-links a {
    color: var(--text-muted);
    font-size: 0.875rem;
}

.copyright {
    text-align: center;
    font-size: 0.875rem;
    color: var(--text-muted);
    border-top: 1px solid var(--border-color);
    padding-top: var(--spacing-sm);
}

/* Responsive */
@media (max-width: 640px) {
    .site-header .container {
        flex-direction: column;
        gap: var(--spacing-sm);
    }

    .hero-section h1 {
        font-size: 2rem;
    }

    .calculator-card {
        padding: var(--spacing-md);
    }

    .primary-result .value {
        font-size: 2rem;
    }
}