:root {
            --primary-color: #2c5f58; /* Teal Green */
            --accent-color: #c9a45c; /* Gold */
            --text-main: #333333;
            --text-light: #666666;
            --bg-body: #f9f9f9;
            --bg-sidebar: #ffffff;
            --border-color: #e0e0e0;
            --shadow: 0 4px 20px rgba(0,0,0,0.05);
            --sidebar-width: 300px;
        }

        [data-theme="dark"] {
            --primary-color: #4db6ac;
            --accent-color: #ffd54f;
            --text-main: #e0e0e0;
            --text-light: #a0a0a0;
            --bg-body: #121212;
            --bg-sidebar: #1e1e1e;
            --border-color: #333333;
            --shadow: 0 4px 20px rgba(0,0,0,0.3);
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            transition: background-color 0.3s, color 0.3s;
        }

        body {
            font-family: 'Inter', sans-serif;
            background-color: var(--bg-body);
            color: var(--text-main);
            line-height: 1.7;
            overflow-x: hidden;
        }

        h1, h2, h3, h4 {
            font-family: 'Merriweather', serif;
            color: var(--text-main);
        }

        a {
            text-decoration: none;
            color: var(--primary-color);
            transition: 0.3s;
        }

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


        /* ফিক্সড অংশ */
        .sidebar-fixed-part {
            flex-shrink: 0;
            padding: 60px 30px 0 30px; /* নিচে প্যাডিং ০ রাখা হয়েছে কারণ social-icons-top প্যাডিং হ্যান্ডেল করবে */
            background: var(--bg-sidebar);
            text-align: center;
            z-index: 5;
        }
        
        /* স্ক্রল অংশ */
        .sidebar-scroll-part {
            flex-grow: 1;
            overflow-y: auto;
            padding: 10px 30px 40px 30px;
        }
        
        /* স্ক্রলবার হাইড বা চিকন করার জন্য */
        .sidebar-scroll-part::-webkit-scrollbar {
            width: 4px;
        }
        .sidebar-scroll-part::-webkit-scrollbar-thumb {
            background-color: var(--border-color);
            border-radius: 10px;
        }


        /* --- Sidebar Navigation --- */
        .sidebar {
            position: fixed;
            top: 0;
            left: 0;
            width: var(--sidebar-width);
            height: 100vh;
            background: var(--bg-sidebar);
            border-right: 1px solid var(--border-color);
            z-index: 1000;
            transition: transform 0.3s ease;
            
            /* নতুন যোগ করা হয়েছে */
            display: flex;
            flex-direction: column;
            overflow: hidden; 
        }

        /* Dark Mode Button - Floating Fixed Position */
        .theme-toggle-btn {
            position: absolute;
            top: 15px;
            right: 15px;
            width: 35px;
            height: 35px;
            border-radius: 50%;
            background: var(--bg-sidebar);
            border: 1px solid var(--border-color);
            color: var(--text-main);
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1rem;
            transition: all 0.3s ease;
            z-index: 1002;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }

        .theme-toggle-btn:hover {
            background: var(--primary-color);
            color: #fff;
            border-color: var(--primary-color);
        }

        .profile-area {
            text-align: center;
            margin-bottom: 10px;
        }

        .profile-img {
            width: 150px;
            height: 150px;
            border-radius: 50%;
            object-fit: cover;
            border: 3px solid var(--primary-color);
            padding: 3px;
            margin-bottom: 15px;
        }

        .name {
            font-size: 1.3rem;
            font-weight: 700;
            margin-bottom: 5px;
            line-height: 1.3;
        }

        .designation {
            font-size: 0.85rem;
            color: var(--text-light);
            font-family: 'Inter', sans-serif;
            margin-bottom: 15px;
            line-height: 1.4;
        }

        /* Social Icons */
        .social-icons-top {
            display: flex;
            justify-content: center;
            gap: 12px;
            margin-bottom: 25px;
            padding-bottom: 20px;
            border-bottom: 1px solid var(--border-color);
        }

        .social-icons-top a {
            font-size: 1.1rem;
            color: var(--text-light);
            width: 35px;
            height: 35px;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 50%;
            border: 1px solid var(--border-color);
            transition: all 0.3s ease;
        }

        .social-icons-top a:hover {
            color: white;
            background-color: var(--primary-color);
            border-color: var(--primary-color);
            transform: translateY(-3px);
        }

        .nav-links {
            list-style: none;
        }

        .nav-links li {
            margin-bottom: 8px;
        }

        .nav-links a {
            color: var(--text-light);
            font-size: 1rem;
            display: flex;
            align-items: center;
            gap: 12px;
            padding: 10px 15px;
            border-radius: 8px; 
        }

        .nav-links a:hover, .nav-links a.active {
            color: var(--primary-color);
            background: transparent;
            font-weight: 600;
        }
        
        .nav-links a.active {
            transform: translateX(5px);
        }

        /* --- Main Content --- */
        .main-content {
            margin-left: var(--sidebar-width);
            padding: 60px 80px;
            max-width: 1200px;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
        }

        section {
            margin-bottom: 100px;
            opacity: 0;
            transform: translateY(20px);
            animation: fadeInUp 0.8s forwards;
        }

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

        .section-title {
            font-size: 2rem;
            margin-bottom: 40px;
            position: relative;
            padding-bottom: 15px;
        }

        .section-title::after {
            content: '';
            position: absolute;
            left: 0;
            bottom: 0;
            width: 60px;
            height: 4px;
            background: var(--accent-color);
        }

        /* --- Hero Section --- */
        .hero-intro {
            font-size: 1.3rem;
            color: var(--primary-color);
            font-weight: 500;
            margin-bottom: 10px;
        }

        .hero-heading {
            font-size: 3.5rem;
            line-height: 1.2;
            margin-bottom: 10px;
        }
        
        .hero-subtitle {
            font-size: 1.2rem;
            font-weight: 400;
            color: var(--text-main);
            margin-bottom: 25px;
            font-family: 'Merriweather', serif;
        }

        .hero-text {
            font-size: 1.1rem;
            color: var(--text-light);
            max-width: 700px;
            margin-bottom: 30px;
            text-align: justify;
        }

        .btn {
            display: inline-block;
            padding: 12px 30px;
            background-color: var(--primary-color);
            color: white;
            border-radius: 5px;
            font-weight: 500;
            border: 2px solid var(--primary-color);
        }

        .btn:hover {
            background-color: transparent;
            color: var(--primary-color);
        }

        .btn-outline {
            background-color: transparent;
            color: var(--text-main);
            border: 2px solid var(--border-color);
            margin-left: 25px; 
        }

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

        /* --- Research Cards --- */
        .interest-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 25px;
        }

        .interest-card {
            background: var(--bg-sidebar);
            padding: 25px;
            border-radius: 10px;
            box-shadow: var(--shadow);
            border: 1px solid var(--border-color);
            text-align: center;
        }

        .interest-card i {
            font-size: 2.5rem;
            color: var(--primary-color);
            margin-bottom: 15px;
        }

        /* --- Education Timeline --- */
        .timeline-item {
            display: flex;
            gap: 30px;
            margin-bottom: 40px;
            position: relative;
        }

        .timeline-year {
            min-width: 120px;
            font-family: 'Merriweather', serif;
            font-weight: 700;
            color: var(--primary-color);
            text-align: right;
            padding-top: 5px;
        }

        .timeline-content {
            border-left: 2px solid var(--border-color);
            padding-left: 30px;
            padding-bottom: 10px;
            position: relative;
        }

        .timeline-content::before {
            content: '';
            position: absolute;
            left: -8px;
            top: 10px;
            width: 14px;
            height: 14px;
            background: var(--bg-sidebar);
            border: 3px solid var(--primary-color);
            border-radius: 50%;
        }

        /* --- Publication List --- */
        .publication-item {
            background: var(--bg-sidebar);
            padding: 20px;
            margin-bottom: 20px;
            border-radius: 8px;
            box-shadow: var(--shadow);
            display: flex;
            gap: 20px;
            align-items: flex-start;
        }

        .pub-icon {
            background: rgba(44, 95, 88, 0.1);
            color: var(--primary-color);
            width: 50px;
            height: 50px;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 5px;
            font-size: 1.2rem;
            flex-shrink: 0;
        }

        .pub-details h4 {
            font-size: 1.1rem;
            margin-bottom: 5px;
        }

        .pub-meta {
            font-size: 0.9rem;
            color: var(--text-light);
            font-style: italic;
        }

        .badge {
            background: var(--accent-color);
            color: #000;
            padding: 2px 8px;
            border-radius: 4px;
            font-size: 0.7rem;
            font-family: 'Inter', sans-serif;
            margin-left: 10px;
            font-style: normal;
        }

        /* --- Contact --- */
        .contact-intro {
            margin-bottom: 40px;
            color: var(--text-light);
        }

        .contact-list {
            display: flex;
            flex-direction: column;
            gap: 25px;
        }

        @media (min-width: 768px) {
            .contact-list {
                flex-direction: row;
                flex-wrap: wrap;
                gap: 50px;
            }
        }

        .contact-info-item {
            display: flex;
            align-items: center;
            gap: 20px;
        }

        .contact-icon-circle {
            width: 50px;
            height: 50px;
            background: transparent;
            border: 1px solid var(--primary-color);
            color: var(--primary-color);
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1.2rem;
            flex-shrink: 0;
        }

        .contact-text h5 {
            font-size: 1.1rem;
            margin-bottom: 2px;
            font-weight: 600;
        }

        .contact-text p, .contact-text a {
            color: var(--text-light);
            font-size: 0.95rem;
        }
        
        .contact-text a:hover {
            color: var(--primary-color);
            text-decoration: underline;
        }

        /* --- Footer --- */
        .footer-copyright {
            margin-top: auto;
            padding-top: 50px;
            padding-bottom: 20px;
            text-align: center;
            border-top: 1px solid var(--border-color);
            color: var(--text-light);
            font-size: 0.9rem;
        }

        /* --- Floating Audio Player --- */
        .audio-player-container {
            position: fixed;
            bottom: 30px;
            right: 30px;
            z-index: 2000; /* Sidebar এর উপরে বা সমান লেভেলে */
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .audio-btn {
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 12px 25px;
            border-radius: 50px;
            font-size: 1rem;
            font-family: 'Inter', sans-serif;
            font-weight: 600;
            cursor: pointer;
            box-shadow: 0 4px 15px rgba(0,0,0,0.2);
            display: flex;
            align-items: center;
            gap: 10px;
            transition: all 0.3s ease;
        }

        .audio-btn:hover {
            transform: scale(1.05);
            background-color: var(--accent-color);
            color: #000;
        }

        .audio-btn i {
            font-size: 1.1rem;
        }

        /* যখন অডিও প্লে হবে তখন এনিমেশন */
        .audio-btn.playing {
            animation: pulse 2s infinite;
        }

        @keyframes pulse {
            0% { box-shadow: 0 0 0 0 rgba(44, 95, 88, 0.7); }
            70% { box-shadow: 0 0 0 10px rgba(44, 95, 88, 0); }
            100% { box-shadow: 0 0 0 0 rgba(44, 95, 88, 0); }
        }

        /* --- Mobile Toggle --- */
        .mobile-toggle {
            display: none;
            position: fixed;
            top: 20px;
            right: 20px;
            z-index: 1100;
            background: var(--primary-color);
            color: white;
            border: none;
            padding: 10px;
            border-radius: 5px;
            font-size: 1.2rem;
            cursor: pointer;
            box-shadow: 0 2px 10px rgba(0,0,0,0.2);
        }

        /* --- Overlay --- */
        .overlay {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.5);
            z-index: 900;
            opacity: 0;
            transition: opacity 0.3s;
        }

        /* --- Responsiveness --- */
        @media (max-width: 992px) {
            .sidebar {
                transform: translateX(-100%);
                width: 280px;
                box-shadow: 0 0 20px rgba(0,0,0,0.5);
            }

            .sidebar.active {
                transform: translateX(0);
            }

            .overlay.active {
                display: block;
                opacity: 1;
            }

            .main-content {
                margin-left: 0;
                padding: 80px 30px;
            }

            .mobile-toggle {
                display: block;
            }

            .hero-heading {
                font-size: 2.5rem;
            }
            
            .cta-buttons .btn {
                margin-bottom: 10px;
            }
            
            .btn-outline {
                margin-left: 10px;
            }

            .timeline-item {
                flex-direction: column;
                gap: 5px;
            }

            .timeline-year {
                text-align: left;
                padding-left: 30px;
            }

            /* মোবাইলে অডিও বাটন একটু ছোট করা */
            .audio-player-container {
                bottom: 20px;
                right: 20px;
            }
            .audio-btn {
                padding: 10px 18px;
                font-size: 0.9rem;
            }
        }
        
        @media (max-width: 480px) {
            .btn-outline {
                margin-left: 0;
                display: block;
                margin-top: 15px;
                text-align: center;
            }
            .btn {
                display: block;
                text-align: center;
            }
        }