:root {
            /* Pastel Palette */
            /* Blue/Purple Range */
            --pastel-blue-dark: #8CA9FF;
            --pastel-blue-light: #AAC4F5;

            /* Yellow/Cream Range */
            --pastel-yellow: #FFF2C6;
            --pastel-cream: #FFF8DE;

            /* Pink/Peach Range */
            --pastel-pink-light: #FFDCDC;
            --pastel-peach-light: #FFF2EB;
            --pastel-beige: #FFE8CD;
            --pastel-peach-dark: #FFD6BA;

            /* Theme Variables */
            --gradient-start: var(--pastel-blue-dark);
            --gradient-end: var(--pastel-peach-dark);
            --accent: var(--pastel-blue-light);

            --bg-start: var(--pastel-cream);
            --bg-end: var(--pastel-peach-light);

            --card-bg: rgba(255, 255, 255, 0.85);

            /* Text Colors - Keeping dark for readability as requested */
            --text-primary: #2d3748;
            --text-secondary: #4a5568;
            --text-muted: #718096;

            /* Shadows - Softened */
            --shadow: 0 8px 32px rgba(140, 169, 255, 0.15);
            --shadow-hover: 0 12px 40px rgba(140, 169, 255, 0.25);
        }

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

        body {
            font-family: 'Poppins', sans-serif;
            background: linear-gradient(135deg, var(--bg-start) 0%, var(--bg-end) 100%);
            min-height: 100vh;
            color: var(--text-primary);
            line-height: 1.6;
            padding: 1rem;
        }

        .container {
            max-width: 1100px;
            margin: 0 auto;
            padding: 1rem;
        }

        /* Language Switcher */
        .lang-switch-container {
            position: absolute;
            top: 1rem;
            right: 1rem;
            z-index: 100;
        }

        .lang-btn {
            font-family: 'Poppins', sans-serif;
            background: var(--card-bg);
            border: 1px solid var(--pastel-blue-light);
            padding: 0.5rem 1rem;
            border-radius: 20px;
            cursor: pointer;
            font-size: 0.85rem;
            font-weight: 600;
            color: var(--text-secondary);
            transition: all 0.3s ease;
            box-shadow: var(--shadow);
        }

        .lang-btn:hover {
            background: var(--pastel-blue-light);
            color: white;
        }

        header {
            text-align: center;
            margin-bottom: 2rem;
            padding: 1.5rem 0;
            position: relative;
        }

        h1 {
            font-size: clamp(1.75rem, 5vw, 2.5rem);
            font-weight: 700;
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            margin-bottom: 0.5rem;
        }

        .subtitle {
            color: var(--text-secondary);
            font-size: clamp(0.9rem, 2.5vw, 1.1rem);
            font-weight: 400;
        }

        /* Tab Navigation */
        .tab-nav {
            display: flex;
            justify-content: center;
            gap: 0.5rem;
            margin-bottom: 2rem;
            flex-wrap: wrap;
        }

        .tab-btn {
            font-family: 'Poppins', sans-serif;
            padding: 0.75rem 1.5rem;
            font-size: 0.95rem;
            font-weight: 600;
            border: none;
            border-radius: 12px;
            cursor: pointer;
            background: var(--card-bg);
            color: var(--text-secondary);
            transition: all 0.3s ease;
            box-shadow: var(--shadow);
            backdrop-filter: blur(10px);
        }

        .tab-btn:hover {
            transform: translateY(-2px);
            box-shadow: var(--shadow-hover);
            background: var(--pastel-pink-light);
        }

        .tab-btn.active {
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            color: white;
        }

        /* Tab Content */
        .tab-content {
            display: none;
            animation: fadeIn 0.4s ease;
        }

        .tab-content.active {
            display: block;
        }

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

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

        /* Cards */
        .card {
            background: var(--card-bg);
            backdrop-filter: blur(10px);
            -webkit-backdrop-filter: blur(10px);
            padding: 1.5rem;
            border-radius: 20px;
            box-shadow: var(--shadow);
            border: 1px solid rgba(255, 255, 255, 0.5);
            position: relative;
            overflow: hidden;
            margin-bottom: 1.5rem;
            transition: all 0.3s ease;
        }

        .card::before {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            height: 4px;
            background: linear-gradient(90deg, var(--gradient-start), var(--accent), var(--gradient-end));
        }

        .card:hover {
            box-shadow: var(--shadow-hover);
        }

        .card h2, .card h3 {
            color: var(--text-primary);
            font-size: 1.25rem;
            font-weight: 600;
            margin-bottom: 0.5rem;
        }

        .card h3 {
             font-size: 1rem;
             display: flex;
             align-items: center;
             gap: 0.5rem;
             margin-bottom: 1rem;
        }

        .card h3::before {
            content: '';
            width: 8px;
            height: 8px;
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            border-radius: 50%;
        }

        .card-description {
            color: var(--text-secondary);
            font-size: 0.9rem;
            margin-bottom: 1.5rem;
        }

        /* Controls */
        .controls {
            display: flex;
            align-items: center;
            gap: 1rem;
            margin-bottom: 1.5rem;
            flex-wrap: wrap;
        }

        .control-group {
            display: flex;
            align-items: center;
            gap: 0.75rem;
        }

        .control-group label {
            font-weight: 500;
            color: var(--text-secondary);
            font-size: 0.9rem;
        }

        input[type="range"] {
            width: 150px;
            height: 8px;
            border-radius: 4px;
            background: linear-gradient(90deg, var(--pastel-blue-light), var(--pastel-peach-dark));
            outline: none;
            -webkit-appearance: none;
            cursor: pointer;
        }

        input[type="range"]::-webkit-slider-thumb {
            -webkit-appearance: none;
            width: 20px;
            height: 20px;
            border-radius: 50%;
            background: white;
            box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
            cursor: pointer;
        }

        input[type="number"] {
            width: 70px;
            padding: 0.5rem 0.75rem;
            font-family: 'Poppins', sans-serif;
            font-size: 1rem;
            font-weight: 600;
            border: 2px solid transparent;
            border-radius: 10px;
            background: rgba(255, 255, 255, 0.9);
            color: var(--text-primary);
            text-align: center;
            transition: all 0.3s ease;
        }

        input[type="number"]:focus {
            outline: none;
            border-color: var(--gradient-start);
            box-shadow: 0 0 0 4px rgba(140, 169, 255, 0.15);
        }

        .value-display {
            font-family: 'Fira Code', monospace;
            font-weight: 600;
            font-size: 1.1rem;
            color: var(--gradient-end);
            min-width: 2rem;
        }

        /* Formula Display & Explanations */
        .formula-box, .explanation {
            background: linear-gradient(135deg, rgba(140, 169, 255, 0.08), rgba(255, 214, 186, 0.08));
            padding: 1rem 1.25rem;
            border-radius: 12px;
            font-family: 'Fira Code', monospace;
            font-size: 0.9rem;
            color: var(--text-secondary);
            border: 1px solid var(--pastel-blue-light);
            margin-bottom: 1.5rem;
        }

        .formula-box .formula {
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--gradient-end);
        }

        .explanation {
            white-space: pre-wrap;
            word-break: break-word;
        }

        .result-big, .result-value {
            font-size: clamp(2rem, 6vw, 3rem);
            font-weight: 700;
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            text-align: center;
            margin: 1rem 0;
            animation: fadeInUp 0.5s ease;
        }

        .result-value {
             font-size: clamp(2rem, 6vw, 2.75rem);
        }

        @keyframes fadeInUp {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        /* ===================== PASCAL'S TRIANGLE ===================== */
        .pascal-container {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 6px;
            padding: 1rem;
            overflow-x: auto;
        }

        .pascal-row {
            display: flex;
            gap: 6px;
            justify-content: center;
        }

        .pascal-cell {
            width: 42px;
            height: 42px;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 10px;
            font-family: 'Fira Code', monospace;
            font-weight: 600;
            font-size: 0.85rem;
            background: linear-gradient(135deg, #edf2f7, #e2e8f0);
            border: 2px solid transparent;
            transition: all 0.25s ease;
            cursor: pointer;
            position: relative;
        }

        .pascal-cell:hover {
            transform: scale(1.1);
            z-index: 10;
        }

        .pascal-cell.highlighted {
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            color: white;
            transform: scale(1.15);
            box-shadow: 0 4px 15px rgba(140, 169, 255, 0.5);
            z-index: 20;
        }

        .pascal-cell.parent {
            background: linear-gradient(135deg, var(--pastel-blue-light), var(--pastel-peach-dark));
            color: white;
            transform: scale(1.1);
            box-shadow: 0 4px 12px rgba(255, 214, 186, 0.5);
            z-index: 15;
        }

        .pascal-tooltip {
            position: fixed;
            background: rgba(45, 55, 72, 0.95);
            color: white;
            padding: 0.75rem 1rem;
            border-radius: 10px;
            font-size: 0.85rem;
            font-family: 'Fira Code', monospace;
            pointer-events: none;
            z-index: 1000;
            opacity: 0;
            transition: opacity 0.2s ease;
            white-space: nowrap;
            box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
        }

        .pascal-tooltip.visible {
            opacity: 1;
        }

        /* ===================== LATTICE PATHS ===================== */
        .lattice-wrapper {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 1.5rem;
        }

        .lattice-grid-container {
            position: relative;
            padding: 2rem;
        }

        .lattice-grid {
            display: grid;
            gap: 0;
        }

        .lattice-cell {
            width: 40px;
            height: 40px;
            border: 1px solid var(--pastel-blue-light);
            background: rgba(255, 255, 255, 0.5);
            position: relative;
        }

        .lattice-cell.origin {
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
        }

        .lattice-cell.destination {
            background: linear-gradient(135deg, var(--pastel-peach-dark), var(--pastel-pink-light));
        }

        .lattice-point {
            position: absolute;
            width: 12px;
            height: 12px;
            background: var(--gradient-end);
            border-radius: 50%;
            top: -6px;
            left: -6px;
            z-index: 5;
        }

        .lattice-cell.origin .lattice-point, .lattice-cell.destination .lattice-point {
            background: white;
        }

        .lattice-path-line {
            position: absolute;
            background: var(--pastel-peach-dark);
            z-index: 3;
            opacity: 0;
            animation: pathDraw 0.3s ease forwards;
        }

        @keyframes pathDraw { to { opacity: 1; } }

        .path-sequence {
            font-family: 'Fira Code', monospace;
            font-size: 1.1rem;
            font-weight: 600;
            letter-spacing: 2px;
            color: var(--gradient-end);
            padding: 0.5rem 1rem;
            background: rgba(140, 169, 255, 0.1);
            border-radius: 8px;
            display: inline-block;
            margin-top: 0.5rem;
        }

        .btn-action {
            font-family: 'Poppins', sans-serif;
            padding: 0.75rem 1.5rem;
            font-size: 0.95rem;
            font-weight: 600;
            border: none;
            border-radius: 12px;
            cursor: pointer;
            background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
            color: white;
            transition: all 0.3s ease;
            box-shadow: 0 4px 15px rgba(140, 169, 255, 0.4);
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 0.5rem;
        }

        .btn-action:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(140, 169, 255, 0.5);
        }

        .btn-clear {
            background: rgba(255, 255, 255, 0.9);
            color: var(--text-secondary);
            border: 2px solid #e2e8f0;
            font-family: 'Poppins', sans-serif;
            padding: 0.75rem 1.5rem;
            font-size: 0.95rem;
            font-weight: 600;
            border-radius: 12px;
            cursor: pointer;
            transition: all 0.3s ease;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 0.5rem;
        }

        .btn-clear:hover {
            background: var(--pastel-pink-light);
            color: var(--text-primary);
            border-color: var(--pastel-peach-dark);
        }

        /* ===================== HANDSHAKE PROBLEM ===================== */
        .handshake-wrapper {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 1.5rem;
        }

        #handshakeCanvas {
            border-radius: 16px;
            background: linear-gradient(135deg, rgba(255, 255, 255, 0.9), rgba(255, 255, 255, 0.7));
            box-shadow: inset 0 2px 10px rgba(0, 0, 0, 0.05);
        }

        .handshake-stats {
            display: flex;
            gap: 2rem;
            flex-wrap: wrap;
            justify-content: center;
        }

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

        .stat-label {
            font-size: 0.85rem;
            color: var(--text-muted);
            margin-bottom: 0.25rem;
        }

        .stat-value {
            font-family: 'Fira Code', monospace;
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--gradient-end);
        }

        /* ===================== PERMUTATION ===================== */
        .input-wrapper {
            display: flex;
            flex-direction: column;
            gap: 1rem;
            background: var(--card-bg);
            padding: 1.5rem;
            border-radius: 20px;
            margin-bottom: 2rem;
            box-shadow: var(--shadow);
            border: 1px solid rgba(255,255,255,0.5);
        }

        @media (min-width: 480px) {
            .input-wrapper {
                flex-direction: row;
                align-items: center;
            }
        }

        input[type="text"] {
            flex: 1;
            padding: 1rem 1.25rem;
            font-size: 1.1rem;
            font-family: 'Poppins', sans-serif;
            font-weight: 600;
            border: 2px solid transparent;
            border-radius: 12px;
            background: rgba(255, 255, 255, 0.9);
            color: var(--text-primary);
            text-transform: uppercase;
            letter-spacing: 3px;
            transition: all 0.3s ease;
            width: 100%;
        }

        input[type="text"]:focus {
            outline: none;
            border-color: var(--gradient-start);
            box-shadow: 0 0 0 4px rgba(140, 169, 255, 0.15);
        }

        .button-group {
            display: flex;
            gap: 0.75rem;
        }

        .result-container {
            display: grid;
            grid-template-columns: 1fr;
            gap: 1.5rem;
            opacity: 0;
            transform: translateY(20px);
            transition: all 0.4s ease;
            pointer-events: none;
        }

        .result-container.visible {
            opacity: 1;
            transform: translateY(0);
            pointer-events: auto;
        }

        @media (min-width: 768px) {
            .result-container {
                grid-template-columns: 1fr 1fr;
            }
        }

        .tile-container {
            display: flex;
            gap: 6px;
            margin-bottom: 1rem;
            flex-wrap: wrap;
        }

        .tile {
            background: linear-gradient(135deg, #edf2f7, #e2e8f0);
            border: 1px solid #cbd5e1;
            padding: 6px 12px;
            border-radius: 8px;
            font-weight: 600;
            font-size: 0.9rem;
            transition: all 0.2s ease;
        }

        .tile.grouped {
            background: linear-gradient(135deg, var(--pastel-blue-light), var(--pastel-pink-light));
            border-color: var(--gradient-start);
            color: var(--text-primary);
        }

        .empty-state {
            text-align: center;
            padding: 3rem 1.5rem;
            color: var(--text-muted);
        }

        .empty-state-icon {
            font-size: 3rem;
            margin-bottom: 1rem;
            opacity: 0.6;
        }

        /* Footer */
        footer {
            text-align: center;
            margin-top: 2rem;
            padding: 1rem;
            color: var(--text-muted);
            font-size: 0.85rem;
        }

        /* Responsive */
        @media (max-width: 600px) {
            .pascal-cell {
                width: 32px;
                height: 32px;
                font-size: 0.7rem;
            }

            .lattice-cell {
                width: 30px;
                height: 30px;
            }

            .controls {
                flex-direction: column;
                align-items: flex-start;
            }

            .lang-switch-container {
                top: 0.5rem;
                right: 0.5rem;
            }
        }

/* Accessibility Focus Styles */
button:focus-visible, input:focus-visible, select:focus-visible {
    outline: 3px solid var(--pastel-blue-dark);
    outline-offset: 2px;
    box-shadow: 0 0 0 4px rgba(140, 169, 255, 0.3);
}

/* Improve contrast for text on colored backgrounds */
.tab-btn.active {
    font-weight: 700;
}