:root {
    --primary: #4f46e5;
    --primary-dark: #4338ca;
    --primary-light: #818cf8;
    --accent: #06b6d4;
    --accent-warm: #f59e0b;
    --success: #10b981;
    --surface: rgba(255, 255, 255, 0.92);
    --surface-solid: #ffffff;
    --text: #1e293b;
    --text-muted: #64748b;
    --border: #e2e8f0;
    --shadow-sm: 0 4px 20px rgba(15, 23, 42, 0.08);
    --shadow-md: 0 12px 40px rgba(15, 23, 42, 0.12);
    --shadow-lg: 0 24px 60px rgba(15, 23, 42, 0.16);
    --radius-sm: 12px;
    --radius-md: 16px;
    --radius-lg: 24px;
    --gradient-bg: linear-gradient(135deg, #0f172a 0%, #312e81 45%, #4f46e5 100%);
    --gradient-brand: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
    --gradient-accent: linear-gradient(135deg, #06b6d4 0%, #3b82f6 100%);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    line-height: 1.6;
    color: var(--text);
    background: var(--gradient-bg);
    background-attachment: fixed;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header Styles - Enhanced Mobile */
.header {
    background: rgba(255, 255, 255, 0.88);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    box-shadow: var(--shadow-sm);
    border-bottom: 1px solid rgba(255, 255, 255, 0.2);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 20px;
}

.logo {
    display: flex;
    align-items: center;
    font-size: 1.35rem;
    font-weight: 700;
    color: var(--primary);
    text-decoration: none;
    letter-spacing: -0.02em;
}

.logo i {
    margin-right: 0.5rem;
    font-size: 1.8rem;
}

.logo-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.logo-icon i {
    margin-right: 0;
    font-size: inherit;
}

.nav-menu {
    display: flex;
    gap: 2rem;
}

.nav-link {
    text-decoration: none;
    color: #333;
    font-weight: 500;
    padding: 0.5rem 1rem;
    border-radius: 25px;
    transition: all 0.3s ease;
}

.nav-link:hover,
.nav-link.active {
    background: var(--gradient-brand);
    color: white;
    transform: translateY(-1px);
    box-shadow: 0 4px 14px rgba(79, 70, 229, 0.35);
}

.mobile-menu-toggle {
    display: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: #667eea;
    background: none;
    border: none;
    padding: 0.5rem;
    border-radius: 8px;
    transition: all 0.3s ease;
}

.mobile-menu-toggle:hover {
    background: rgba(102, 126, 234, 0.1);
    transform: scale(1.1);
}

/* Hero Section */
.hero {
    padding: 3.5rem 0 2.5rem;
    color: white;
}

.hero-grid {
    display: grid;
    grid-template-columns: 1.2fr 0.8fr;
    gap: 2.5rem;
    align-items: center;
}

.hero-content {
    text-align: left;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background: rgba(255, 255, 255, 0.12);
    border: 1px solid rgba(255, 255, 255, 0.2);
    padding: 0.45rem 1rem;
    border-radius: 999px;
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: 1.25rem;
    backdrop-filter: blur(8px);
}

.hero h1 {
    font-size: clamp(2rem, 5vw, 3.25rem);
    font-weight: 800;
    margin-bottom: 1rem;
    text-shadow: none;
    line-height: 1.15;
    letter-spacing: -0.03em;
}

.hero p {
    font-size: 1.1rem;
    opacity: 0.92;
    max-width: 540px;
    margin: 0 0 1.5rem;
    line-height: 1.7;
}

.hero-highlight {
    background: var(--gradient-accent);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    font-weight: 800;
}

.hero-trust {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    margin-bottom: 1.75rem;
}

.hero-trust span {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    font-size: 0.9rem;
    font-weight: 500;
    opacity: 0.9;
}

.hero-trust i {
    color: var(--accent);
}

.site-search {
    position: relative;
    max-width: 480px;
}

.site-search i {
    position: absolute;
    left: 1.1rem;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-muted);
    pointer-events: none;
}

.site-search input {
    width: 100%;
    padding: 1rem 1rem 1rem 2.75rem;
    border: 2px solid rgba(255, 255, 255, 0.15);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, 0.95);
    font-size: 1rem;
    color: var(--text);
    box-shadow: var(--shadow-md);
    transition: border-color 0.2s, box-shadow 0.2s;
}

.site-search input:focus {
    outline: none;
    border-color: var(--primary-light);
    box-shadow: 0 0 0 4px rgba(79, 70, 229, 0.15), var(--shadow-md);
}

.search-results {
    position: absolute;
    top: calc(100% + 8px);
    left: 0;
    right: 0;
    background: white;
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    overflow: hidden;
    z-index: 100;
    max-height: 320px;
    overflow-y: auto;
}

.search-result {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.85rem 1.1rem;
    color: var(--text);
    text-decoration: none;
    border-bottom: 1px solid var(--border);
    transition: background 0.15s;
}

.search-result:hover {
    background: #f8fafc;
    color: var(--primary);
}

.search-result i {
    color: var(--primary);
    width: 1.25rem;
}

.search-empty {
    padding: 1rem;
    color: var(--text-muted);
    text-align: center;
    font-size: 0.9rem;
}

.hero-popular {
    background: rgba(255, 255, 255, 0.08);
    border: 1px solid rgba(255, 255, 255, 0.12);
    border-radius: var(--radius-lg);
    padding: 1.75rem;
    backdrop-filter: blur(12px);
}

.hero-popular h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 1rem;
    opacity: 0.9;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.popular-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 0.6rem;
}

.popular-chip {
    display: inline-flex;
    align-items: center;
    gap: 0.45rem;
    padding: 0.55rem 1rem;
    background: rgba(255, 255, 255, 0.12);
    border: 1px solid rgba(255, 255, 255, 0.18);
    border-radius: 999px;
    color: white;
    text-decoration: none;
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.2s ease;
}

.popular-chip:hover {
    background: white;
    color: var(--primary);
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

/* Calculator Section - IMPROVED WITH FACEBOOK COMMENTS SUPPORT */
.calculator-section {
    padding: 2rem 0;
    display: flex;
    justify-content: center;
    margin-bottom: 2rem; /* Space for Facebook comments */
}

.calculator-wrapper {
    display: flex;
    justify-content: center;
    align-items: flex-start;
    gap: 2rem;
    flex-wrap: wrap;
    max-width: 900px;
    width: 100%;
    position: relative;
    z-index: 1; /* Ensure proper stacking */
}

.calculator {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-radius: 24px;
    padding: 2rem;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.15);
    width: 380px;
    max-width: 100%;
    margin: 0 auto;
}

/* Calculator Display - IMPROVED */
.calculator-display {
    background: linear-gradient(145deg, #1e1e1e, #2a2a2a);
    border-radius: 20px;
    padding: 2rem 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: inset 0 4px 8px rgba(0, 0, 0, 0.3);
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.display-screen {
    text-align: right;
    color: white;
}

.previous-operand {
    font-size: 1rem;
    opacity: 0.6;
    min-height: 1.5rem;
    margin-bottom: 0.5rem;
    word-wrap: break-word;
}

.current-operand {
    font-size: 2.2rem;
    font-weight: 600;
    word-wrap: break-word;
    word-break: break-all;
    line-height: 1.2;
    min-height: 2.6rem;
}

/* Calculator Buttons - LAYOUT MỚI */
.calculator-buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(5, 1fr);
    gap: 12px;
    aspect-ratio: 1;
    width: 100%;
}

.btn {
    border: none;
    border-radius: 16px;
    font-size: 1.3rem;
    font-weight: 600;
    height: 100%;
    min-height: 60px;
    cursor: pointer;
    transition: all 0.15s ease;
    font-family: inherit;
    display: flex;
    align-items: center;
    justify-content: center;
    user-select: none;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(255, 255, 255, 0.1);
    opacity: 0;
    transition: opacity 0.15s ease;
}

.btn:hover::before {
    opacity: 1;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
}

.btn:active {
    transform: translateY(0);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

/* Button Types - IMPROVED */
.btn-number {
    background: linear-gradient(145deg, #ffffff, #f8f9fa);
    color: #333;
    border: 2px solid #e9ecef;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.btn-operator {
    background: linear-gradient(145deg, #667eea, #764ba2);
    color: white;
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.3);
}

.btn-function {
    background: linear-gradient(145deg, #6c757d, #5a6268);
    color: white;
    box-shadow: 0 4px 12px rgba(108, 117, 125, 0.3);
}

.btn-equals {
    background: linear-gradient(145deg, #28a745, #20c997);
    color: white;
    box-shadow: 0 4px 12px rgba(40, 167, 69, 0.3);
}

/* Special Button Layouts - CHỈ CÒN ZERO WIDE */
.btn-zero-wide {
    grid-column: span 2;
}

/* History Panel - IMPROVED WITH COMMENTS COMPATIBILITY */
.history-panel {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-radius: 24px;
    padding: 1.5rem;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
    width: 320px;
    max-height: 520px;
    flex-shrink: 0;
    position: relative;
    z-index: 2; /* Higher than Facebook comments */
    margin-bottom: 1rem; /* Extra space at bottom */
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
    padding-bottom: 0.75rem;
    border-bottom: 2px solid #e9ecef;
}

.history-header h3 {
    color: #333;
    font-size: 1.2rem;
    margin: 0;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.btn-clear-history {
    background: linear-gradient(145deg, #dc3545, #c82333);
    color: white;
    border: none;
    border-radius: 10px;
    padding: 0.5rem 0.75rem;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: 0 2px 8px rgba(220, 53, 69, 0.3);
}

.btn-clear-history:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(220, 53, 69, 0.4);
}

.history-list {
    max-height: 420px;
    overflow-y: auto;
    padding-right: 8px;
}

.history-list::-webkit-scrollbar {
    width: 6px;
}

.history-list::-webkit-scrollbar-track {
    background: #f1f1f1;
    border-radius: 3px;
}

.history-list::-webkit-scrollbar-thumb {
    background: #c1c1c1;
    border-radius: 3px;
}

.history-list::-webkit-scrollbar-thumb:hover {
    background: #a8a8a8;
}

.history-empty {
    text-align: center;
    color: #666;
    padding: 3rem 1rem;
    font-style: italic;
}

.history-item {
    background: linear-gradient(145deg, #f8f9fa, #e9ecef);
    border-radius: 12px;
    padding: 1rem;
    margin-bottom: 0.8rem;
    cursor: pointer;
    transition: all 0.3s ease;
    border: 2px solid transparent;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

.history-item:hover {
    background: linear-gradient(145deg, #e9ecef, #dee2e6);
    border-color: #667eea;
    transform: translateX(8px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.history-calculation {
    font-family: 'Courier New', monospace;
    color: #495057;
    font-weight: 600;
    font-size: 0.9rem;
}

.history-result {
    font-family: 'Courier New', monospace;
    color: #667eea;
    font-size: 1.1rem;
    font-weight: 700;
    margin-top: 0.4rem;
}

.history-time {
    font-size: 0.75rem;
    color: #6c757d;
    margin-top: 0.4rem;
}

/* Facebook Comments Section */
.comments-section {
    margin-top: 3rem;
    clear: both;
    position: relative;
    z-index: 0;
}

.comments-section::after {
    content: "";
    display: table;
    clear: both;
}

.fb-comments {
    margin: 2rem 0;
    padding: 1.5rem;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-radius: 16px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.08);
    position: relative;
    z-index: 0; /* Lower than calculator */
    clear: both; /* Ensure it appears below floating elements */
}

.fb-comments iframe {
    width: 100% !important;
    max-width: 100% !important;
    overflow: hidden;
    display: block;
    clear: both;
}

/* Comments Section Title (Optional) */
.comments-section::before {
    content: "💬 Community Discussion";
    text-align: center;
    font-size: 1.2rem;
    font-weight: 600;
    color: #ffffff;
    margin-bottom: 1rem;
    padding: 1rem;
}

.comments-load-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0.5rem auto 1rem;
    width: max-content;
    padding: 0.7rem 1.2rem;
    border: none;
    border-radius: 999px;
    background: linear-gradient(135deg, #4267b2, #365899);
    color: #fff;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s ease, opacity 0.2s ease;
}

.comments-load-btn:hover {
    transform: translateY(-1px);
}

.comments-load-btn:disabled {
    opacity: 0.75;
    cursor: wait;
}

.fb-comments-pending {
    min-height: 180px;
}

/* Categories Section */
.categories {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    margin: 2rem 0;
    border-radius: 20px;
    padding: 3rem 0;
}

.categories h2 {
    text-align: center;
    font-size: 2.5rem;
    margin-bottom: 3rem;
    color: #333;
}

.categories-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.category-card {
    background: white;
    border-radius: 15px;
    padding: 2rem;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
    border: 2px solid transparent;
}

.category-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.15);
    border-color: #667eea;
}

.category-icon {
    width: 60px;
    height: 60px;
    background: linear-gradient(135deg, #667eea, #764ba2);
    border-radius: 15px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 1.5rem;
}

.category-icon i {
    font-size: 1.8rem;
    color: white;
}

.category-card h3 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: #333;
}

.category-card p {
    color: #666;
    margin-bottom: 1.5rem;
}

.category-list {
    list-style: none;
}

.category-list li {
    margin-bottom: 0.8rem;
}

.category-list a {
    text-decoration: none;
    color: var(--primary);
    font-weight: 500;
    transition: color 0.3s ease;
}

.category-list a:hover {
    color: var(--primary-dark);
    text-decoration: underline;
}

.view-all-link {
    color: var(--primary);
    text-decoration: none;
    font-weight: 600;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
}

.view-all-link:hover {
    color: #0056b3;
    transform: translateX(3px);
}

.view-all-link::after {
    content: "→";
    font-weight: bold;
    transition: transform 0.3s ease;
}

.view-all-link:hover::after {
    transform: translateX(3px);
}

.category-list .view-all-link {
    font-style: italic;
    border: 1px solid #007bff;
    padding: 0.3rem 0.8rem;
    border-radius: 15px;
    background: rgba(0, 123, 255, 0.1);
    font-size: 0.9rem;
}

.category-list .view-all-link:hover {
    background: rgba(0, 123, 255, 0.2);
    border-color: #0056b3;
}

/* Footer */
.footer {
    background: #1a1a1a;
    color: white;
    padding: 3rem 0 1rem;
    margin-top: 2rem;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-section h4 {
    font-size: 1.2rem;
    margin-bottom: 1rem;
    color: #667eea;
}

.footer-section ul {
    list-style: none;
}

.footer-section li {
    margin-bottom: 0.5rem;
}

.footer-section a {
    text-decoration: none;
    color: #ccc;
    transition: color 0.3s ease;
}

.footer-section a:hover {
    color: #667eea;
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid #333;
    color: #999;
}

/* Responsive Design - ENHANCED MOBILE OPTIMIZATION */
@media (max-width: 768px) {
    .header .container {
        padding: 0.75rem 15px;
    }
    
    .logo {
        font-size: 1.3rem;
    }
    
    .logo i {
        font-size: 1.6rem;
        margin-right: 0.4rem;
    }
    
    .nav-menu {
        display: none;
    }
    
    .mobile-menu-toggle {
        display: block;
        font-size: 1.4rem;
        padding: 0.4rem;
    }
    
    /* Enhanced Hero Section for Mobile */
    .hero {
        padding: 2rem 0 1.5rem;
        text-align: center;
    }
    
    .hero h1 {
        font-size: 1.75rem;
        line-height: 1.3;
        margin-bottom: 1rem;
        padding: 0 1rem;
    }
    
    .hero p {
        font-size: 0.95rem;
        line-height: 1.5;
        padding: 0 1rem;
        max-width: 90%;
        margin: 0 auto;
    }
    
    /* Enhanced Calculator Section */
    .calculator-section {
        padding: 1.5rem 0;
        margin-bottom: 3rem; /* More space before comments on mobile */
    }
    
    .calculator-wrapper {
        flex-direction: column;
        align-items: center;
        gap: 1.5rem;
        margin-bottom: 2rem; /* Extra space on mobile */
    }
    
    /* Facebook Comments Mobile */
    .comments-section {
        margin-top: 2rem;
        position: relative;
        clear: both;
        z-index: -1; /* Below all calculator elements */
    }
    
    .comments-section::before {
        font-size: 1.1rem;
        padding: 0.8rem;
    }
    
    .fb-comments {
        margin: 1.5rem 0.5rem;
        padding: 1rem;
        border-radius: 12px;
        position: relative;
        z-index: -1; /* Below calculator elements */
    }
    
    .calculator {
        width: 100%;
        max-width: 350px;
        padding: 1.25rem;
        border-radius: 20px;
    }
    
    .calculator-display {
        padding: 1.25rem 1rem;
        margin-bottom: 1.25rem;
        border-radius: 16px;
        min-height: 90px;
    }
    
    .calculator-buttons {
        gap: 8px;
    }
    
    .btn {
        font-size: 1rem;
        min-height: 52px;
        border-radius: 14px;
    }
    
    .current-operand {
        font-size: 1.9rem;
        line-height: 1.2;
    }
    
    .previous-operand {
        font-size: 0.9rem;
    }
    
    .history-panel {
        width: 100%;
        max-width: 350px;
        max-height: 280px;
        border-radius: 20px;
        margin-bottom: 3rem; /* Extra space for Facebook comments */
        position: relative;
        z-index: 2;
    }
    
    /* Enhanced Categories Section */
    .categories {
        margin: 1.5rem 0.5rem;
        padding: 2rem 1rem;
        border-radius: 16px;
    }
    
    .categories h2 {
        font-size: 1.8rem;
        margin-bottom: 2rem;
    }
    
    .categories-grid {
        grid-template-columns: 1fr;
        gap: 1.25rem;
    }
    
    .category-card {
        padding: 1.25rem;
        border-radius: 12px;
        box-shadow: 0 6px 20px rgba(0, 0, 0, 0.08);
    }
    
    .category-card:hover {
        transform: translateY(-2px);
        box-shadow: 0 8px 25px rgba(0, 0, 0, 0.12);
    }
    
    .category-icon {
        width: 50px;
        height: 50px;
        border-radius: 12px;
        margin-bottom: 1rem;
    }
    
    .category-icon i {
        font-size: 1.5rem;
    }
    
    .category-card h3 {
        font-size: 1.3rem;
        margin-bottom: 0.75rem;
    }
    
    .category-card p {
        font-size: 0.9rem;
        margin-bottom: 1.25rem;
        line-height: 1.4;
    }
    
    .category-list li {
        margin-bottom: 0.6rem;
    }
    
    .category-list a {
        font-size: 0.9rem;
        line-height: 1.4;
    }
    
    /* Enhanced Footer */
    .footer {
        padding: 2rem 0 1rem;
        margin-top: 1.5rem;
    }
    
    .footer-content {
        grid-template-columns: repeat(2, 1fr);
        gap: 1.5rem;
        margin-bottom: 1.5rem;
    }
    
    .footer-section h4 {
        font-size: 1.1rem;
        margin-bottom: 0.8rem;
    }
    
    .footer-section a {
        font-size: 0.9rem;
    }
    
    .footer-bottom {
        padding-top: 1.5rem;
        font-size: 0.85rem;
        line-height: 1.4;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 12px;
    }
    
    /* Enhanced header for small screens */
    .header .container {
        padding: 0.6rem 12px;
    }
    
    .logo {
        font-size: 1.2rem;
    }
    
    .logo i {
        font-size: 1.4rem;
        margin-right: 0.3rem;
    }
    
    .mobile-menu-toggle {
        font-size: 1.3rem;
        padding: 0.3rem;
    }
    
    /* Ultra-compact mobile design */
    .hero {
        padding: 1.5rem 0 1rem;
    }
    
    .hero h1 {
        font-size: 1.5rem;
        line-height: 1.25;
        padding: 0 0.5rem;
    }
    
    .hero p {
        font-size: 0.9rem;
        padding: 0 0.5rem;
        max-width: 95%;
    }
    
    .calculator-section {
        padding: 1rem 0;
        margin-bottom: 3rem; /* More space before comments on mobile */
    }
    
    /* Ultra-compact Facebook Comments */
    .comments-section {
        margin-top: 1.5rem;
        position: relative;
        clear: both;
        z-index: -1; /* Below all calculator elements */
    }
    
    .comments-section::before {
        font-size: 1rem;
        padding: 0.6rem;
        margin-bottom: 0.8rem;
    }
    
    .fb-comments {
        margin: 1rem 0.25rem;
        padding: 0.75rem;
        border-radius: 10px;
        position: relative;
        z-index: -1; /* Below calculator elements */
    }
    
    .calculator {
        padding: 1rem;
        border-radius: 18px;
        max-width: 320px;
    }
    
    .calculator-display {
        padding: 1rem 0.8rem;
        border-radius: 14px;
        min-height: 80px;
    }
    
    .current-operand {
        font-size: 1.7rem;
    }
    
    .previous-operand {
        font-size: 0.8rem;
    }
    
    .calculator-buttons {
        gap: 6px;
    }
    
    .btn {
        font-size: 0.95rem;
        min-height: 48px;
        border-radius: 12px;
    }
    
    .history-panel {
        border-radius: 18px;
        max-width: 320px;
        max-height: 250px;
        margin-bottom: 3rem; /* Ensure space for Facebook comments */
        position: relative;
        z-index: 2;
    }
    
    /* Ultra-compact categories */
    .categories {
        margin: 1rem 0.25rem;
        padding: 1.5rem 0.75rem;
        border-radius: 14px;
    }
    
    .categories h2 {
        font-size: 1.6rem;
        margin-bottom: 1.5rem;
    }
    
    .categories-grid {
        gap: 1rem;
    }
    
    .category-card {
        padding: 1rem;
        border-radius: 10px;
    }
    
    .category-icon {
        width: 45px;
        height: 45px;
        border-radius: 10px;
        margin-bottom: 0.8rem;
    }
    
    .category-icon i {
        font-size: 1.3rem;
    }
    
    .category-card h3 {
        font-size: 1.2rem;
        margin-bottom: 0.6rem;
    }
    
    .category-card p {
        font-size: 0.85rem;
        margin-bottom: 1rem;
        line-height: 1.3;
    }
    
    .category-list li {
        margin-bottom: 0.5rem;
    }
    
    .category-list a {
        font-size: 0.85rem;
    }
    
    /* Ultra-compact footer */
    .footer {
        padding: 1.5rem 0 0.8rem;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        gap: 1.2rem;
        margin-bottom: 1.2rem;
    }
    
    .footer-section {
        text-align: center;
    }
    
    .footer-section h4 {
        font-size: 1rem;
        margin-bottom: 0.6rem;
    }
    
    .footer-section ul {
        display: flex;
        flex-wrap: wrap;
        justify-content: center;
        gap: 0.8rem;
    }
    
    .footer-section li {
        margin-bottom: 0;
    }
    
    .footer-section a {
        font-size: 0.8rem;
        padding: 0.3rem 0.6rem;
        background: rgba(102, 126, 234, 0.1);
        border-radius: 8px;
        transition: all 0.3s ease;
    }
    
    .footer-section a:hover {
        background: rgba(102, 126, 234, 0.2);
        transform: translateY(-1px);
    }
    
    .footer-bottom {
        padding-top: 1.2rem;
        font-size: 0.8rem;
    }
    
    .footer-bottom p {
        margin-bottom: 0.4rem;
    }
}

/* Animations - IMPROVED */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes slideInLeft {
    from {
        opacity: 0;
        transform: translateX(-30px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

@keyframes slideInRight {
    from {
        opacity: 0;
        transform: translateX(30px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.calculator {
    animation: slideInLeft 0.6s ease;
}

.history-panel {
    animation: slideInRight 0.6s ease;
}

.category-card {
    animation: fadeInUp 0.6s ease;
}

.category-card:nth-child(2) {
    animation-delay: 0.1s;
}

.category-card:nth-child(3) {
    animation-delay: 0.2s;
}

.category-card:nth-child(4) {
    animation-delay: 0.3s;
}

/* Enhanced Touch Interactions */
.btn:active {
    animation: buttonPress 0.1s ease;
}

.category-card:active,
.nav-link:active,
.mobile-menu-toggle:active {
    transform: scale(0.98);
}

@keyframes buttonPress {
    0% { transform: scale(1) translateY(-2px); }
    50% { transform: scale(0.95) translateY(0); }
    100% { transform: scale(1) translateY(0); }
}

/* Mobile Performance Optimizations */
@media (max-width: 768px) {
    * {
        -webkit-tap-highlight-color: transparent;
        -webkit-touch-callout: none;
        -webkit-user-select: none;
        user-select: none;
    }
    
    input, textarea {
        -webkit-user-select: text;
        user-select: text;
    }
    
    .category-card,
    .btn,
    .nav-link,
    .mobile-menu-toggle {
        touch-action: manipulation;
    }
    
    /* Smooth scrolling */
    html {
        scroll-behavior: smooth;
        -webkit-overflow-scrolling: touch;
    }
    
    /* Prevent zoom on inputs */
    input[type="text"],
    input[type="number"],
    select,
    textarea {
        font-size: 16px !important;
    }

    .hero-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }

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

    .hero-trust,
    .popular-chips {
        justify-content: center;
    }

    .site-search {
        margin: 0 auto;
    }
}

/* Shared calculator page styles */
.main .hero {
    padding: 2.5rem 0 1.5rem;
    text-align: center;
}

.main .hero h1 {
    font-size: clamp(1.75rem, 4vw, 2.5rem);
    font-weight: 800;
    letter-spacing: -0.02em;
}

.main .hero p {
    margin: 0 auto;
    max-width: 640px;
    opacity: 0.9;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--text);
    font-size: 0.925rem;
}

.input-group input,
.input-group select,
.input-group textarea {
    width: 100%;
    padding: 0.9rem 1rem;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-family: inherit;
    background: white;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.input-group input:focus,
.input-group select:focus,
.input-group textarea:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 4px rgba(79, 70, 229, 0.12);
}

.calculate-btn,
button.calculate-btn,
input[type="submit"].calculate-btn {
    background: var(--gradient-brand);
    color: white;
    border: none;
    padding: 1rem 2rem;
    border-radius: var(--radius-sm);
    font-size: 1.05rem;
    font-weight: 600;
    cursor: pointer;
    width: 100%;
    transition: transform 0.2s, box-shadow 0.2s;
    box-shadow: 0 8px 24px rgba(79, 70, 229, 0.25);
}

.calculate-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 12px 32px rgba(79, 70, 229, 0.35);
}

.result-section,
.result-card,
[class*="-calculator"]:not(.category-card) {
    scroll-margin-top: 100px;
}

.categories {
    background: var(--surface);
    backdrop-filter: blur(16px);
    border: 1px solid rgba(255, 255, 255, 0.5);
}

.category-card {
    border: 1px solid var(--border);
    transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

.category-card:hover {
    border-color: var(--primary-light);
    transform: translateY(-6px);
}

.category-icon {
    background: var(--gradient-brand);
}

.category-icon-construction {
    background: linear-gradient(135deg, #f59e0b 0%, #d97706 100%);
}

.category-icon-utilities {
    background: linear-gradient(135deg, #06b6d4 0%, #0891b2 100%);
}

.footer-section h4 {
    color: var(--primary-light);
}

.btn-operator {
    background: var(--gradient-brand);
}

.btn-equals {
    background: linear-gradient(135deg, var(--success) 0%, #059669 100%);
}

.calculator,
.history-panel,
[class$="-calculator"],
form[class*="calculator"] {
    border: 1px solid rgba(255, 255, 255, 0.6);
}

@media (max-width: 768px) {
    .nav-menu {
        border-top: 1px solid var(--border);
    }
}