:root {
            --primary-color: #f57f17;
            --secondary-color: #fbc02d;
            --bg-color: #f4f7f6;
            --sidebar-bg: #f9a825;
            --text-color: #333;
            --white: #ffffff;
            --border-radius: 8px;
            --shadow: 0 4px 6px rgba(0,0,0,0.1);
        }
        * {
            box-sizing: border-box;
            margin: 0;
            font-family: "vazirmatn", 'Tahoma', 'Segoe UI', Geneva, Verdana, sans-serif;
            padding: 0;
        }
        body[lang="fa"] {
            font-family: "vazirmatn", 'Tahoma', 'Segoe UI', Geneva, Verdana, sans-serif;
        }
        body[lang="en"] {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        body {
            background-color: var(--bg-color);
            color: var(--text-color);
            display: flex;
            flex-direction: column;
            height: 100vh;
            overflow: hidden;
        }
        .top-bar {
            background-color: var(--sidebar-bg);
            color: var(--white);
            padding: 10px 20px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            box-shadow: 0 2px 4px rgba(0,0,0,0.1);
            z-index: 10;
        }
        .lang-btn {
            background: rgba(255,255,255,0.2);
            border: 1px solid rgba(255,255,255,0.4);
            color: white;
            padding: 5px 15px;
            border-radius: 4px;
            cursor: pointer;
            font-size: 0.9rem;
            transition: background 0.3s;
        }
        .lang-btn:hover {
            background: rgba(255,255,255,0.4);
        }
        .app-container {
            display: flex;
            flex: 1;
            overflow: hidden;
        }
        .sidebar {
            width: 280px;
            background-color: var(--sidebar-bg);
            color: var(--white);
            display: flex;
            flex-direction: column;
            padding: 20px;
            overflow-y: auto;
            transition: all 0.3s ease;
            flex-shrink: 0;
        }
        .sidebar h2 {
            font-size: 1.2rem;
            margin-bottom: 30px;
            text-align: center;
            border-bottom: 1px solid rgba(255,255,255,0.2);
            padding-bottom: 15px;
        }
        .nav-btn {
            background: none;
            border: none;
            color: rgba(255,255,255,0.9);
            padding: 12px 15px;
            text-align: inherit;
            cursor: pointer;
            font-size: 0.95rem;
            border-radius: var(--border-radius);
            margin-bottom: 8px;
            transition: background 0.2s, color 0.2s;
        }
        .nav-btn:hover {
            background-color: rgba(255,255,255,0.2);
            color: var(--white);
        }
        .nav-btn.active {
            background-color: var(--secondary-color);
            color: #333;
            font-weight: bold;
        }
        .main-content {
            flex: 1;
            padding: 40px;
            overflow-y: auto;
            position: relative;
        }
        .tool-container {
            display: none;
            background: var(--white);
            padding: 30px;
            border-radius: var(--border-radius);
            box-shadow: var(--shadow);
            max-width: 850px;
            margin: 0 auto;
            animation: fadeIn 0.4s ease-in-out;
        }
        .tool-container.active {
            display: block;
        }
        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }
        .tool-header {
            margin-bottom: 25px;
            border-bottom: 2px solid var(--bg-color);
            padding-bottom: 15px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
            gap: 10px;
        }
        .tool-header h1 {
            color: var(--primary-color);
            font-size: 1.5rem;
        }
        .tool-header p {
            color: #666;
            font-size: 0.9rem;
            margin-top: 5px;
        }
        .form-group {
            margin-bottom: 20px;
        }
        .form-group label {
            display: block;
            margin-bottom: 8px;
            font-weight: bold;
            font-size: 0.9rem;
        }
        .form-group input {
            width: 100%;
            padding: 10px;
            border: 1px solid #ddd;
            border-radius: var(--border-radius);
            font-size: 1rem;
            transition: border-color 0.3s;
        }
        .form-group input:focus {
            border-color: var(--secondary-color);
            outline: none;
        }
        .calc-btn {
            background-color: var(--primary-color);
            color: var(--white);
            border: none;
            padding: 12px 25px;
            font-size: 1rem;
            border-radius: var(--border-radius);
            cursor: pointer;
            width: 100%;
            transition: background 0.3s;
            margin-top: 10px;
        }
        .calc-btn:hover {
            background-color: #e65100;
        }
        .print-btn {
            background-color: #555;
            color: white;
            border: none;
            padding: 8px 15px;
            border-radius: 4px;
            cursor: pointer;
            font-size: 0.85rem;
        }
        .print-btn:hover { background-color: #333; }
        
        .result-box {
            margin-top: 30px;
            padding: 20px;
            background-color: #fffde7;
            border: 1px solid #fff9c4;
            border-radius: var(--border-radius);
            display: none;
        }
        .result-box h3 {
            color: var(--primary-color);
            margin-bottom: 10px;
            font-size: 1.1rem;
        }
        .result-value {
            font-size: 1.2rem;
            font-weight: bold;
            color: #f57f17;
        }
        .steps-box {
            margin-top: 20px;
            padding: 20px;
            background-color: #e3f2fd;
            border: 1px solid #bbdefb;
            border-radius: var(--border-radius);
            display: none;
        }
        .steps-box h4 {
            color: #0277bd;
            margin-bottom: 15px;
            font-size: 1rem;
            border-bottom: 1px solid #bbdefb;
            padding-bottom: 8px;
        }
        .step-item {
            margin-bottom: 12px;
            font-size: 0.95rem;
            line-height: 1.6;
        }
        .step-item strong {
            color: #01579b;
        }
        .formula {
            font-family: 'Courier New', Courier, monospace;
            background: rgba(255,255,255,0.6);
            padding: 2px 6px;
            border-radius: 4px;
            direction: ltr;
            display: inline-block;
        }
        /* Scrollbar */
        ::-webkit-scrollbar { width: 10px; height: 10px; }
        ::-webkit-scrollbar-track { background: rgba(0, 0, 0, 0.05); border-radius: 10px; }
        ::-webkit-scrollbar-thumb { background: var(--secondary-color); border-radius: 10px; border: 2px solid var(--bg-color); }
        ::-webkit-scrollbar-thumb:hover { background: var(--primary-color); }
        * { scrollbar-width: thin; scrollbar-color: var(--secondary-color) var(--bg-color); }

        @media (max-width: 768px) {
            .app-container { flex-direction: column; }
            .sidebar { width: 100%; flex-direction: row; overflow-x: auto; padding: 10px; align-items: center; height: auto; flex-shrink: 0; white-space: nowrap; }
            .sidebar h2 { display: none; }
            .nav-btn { margin-bottom: 0; margin-left: 10px; font-size: 0.85rem; padding: 8px 12px; }
            html[dir="ltr"] .nav-btn { margin-left: 0; margin-right: 10px; }
            .main-content { padding: 20px; }
            .tool-header { flex-direction: column; align-items: flex-start; }
            .print-btn { width: 100%; margin-top: 10px; }
        }
        @media print {
            .top-bar, .sidebar, .calc-btn, .print-btn { display: none !important; }
            body { background-color: white; height: auto; overflow: visible; display: block; }
            .app-container { display: block; }
            .main-content { padding: 0; overflow: visible; }
            .tool-container { box-shadow: none; border: 1px solid #ddd; max-width: 100%; display: block !important; }
            .tool-container:not(.active) { display: none !important; }
            .steps-box, .result-box { display: block !important; border: 1px solid #ccc; background: none; }
        }