* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            /* Deep navy background */
            background-color: #0a2e4d;
            /* Your transparent background.png layered on top */
            background-image: url('./resources/background.png');
            background-size: cover;
            background-position: center;
            background-attachment: fixed;
            background-repeat: no-repeat;
            min-height: 100vh;
            padding: 0;
            color: #e3f2fd; /* Light ice blue — clean and readable */
        }
        
        .title-container {
            text-align: center;
            padding: 20px 0;
        }
        
        .title-image {
            max-width: 800px;
            max-height: 200px;
            height: auto;
            width: auto;
            display: inline-block;
            object-fit: contain;
            box-shadow: 0 8px 25px rgba(0, 20, 40, 0.4);
            border-radius: 12px;
        }
        
        .container {
            max-width: 900px;
            margin: 0 auto 30px auto;
            background: rgba(227, 242, 253, 0.08);
            backdrop-filter: blur(10px);
            border-radius: 20px;
            box-shadow: 0 15px 35px rgba(0, 20, 40, 0.3);
            padding: 30px;
            border: 1px solid rgba(187, 222, 251, 0.2);
        }
        
        .header {
            text-align: center;
            margin-bottom: 30px;
            padding: 10px 0;
        }
        
        h1 {
            font-size: 2.5rem;
            font-weight: 800;
            margin-bottom: 15px;
            color: #bbdefb; /* Soft sky blue — elegant */
            text-shadow: 1px 1px 3px rgba(0, 0, 0, 0.4);
        }
        
        .controls {
            background: rgba(187, 222, 251, 0.15);
            border-radius: 16px;
            padding: 20px;
            box-shadow: 0 10px 25px rgba(0, 20, 40, 0.15);
            margin-bottom: 30px;
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            align-items: center;
            gap: 15px;
            border: 1px solid rgba(187, 222, 251, 0.2);
        }
        
        .btn {
            padding: 10px 20px;
            border-radius: 10px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            border: none;
            font-size: 0.95rem;
        }
        
        .btn-primary {
            background: #64b5f6; /* Bright sky blue */
            color: #0a2e4d;
        }
        
        .btn-primary:hover {
            background: #42a5f5;
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(100, 181, 246, 0.3);
        }
        
        .btn-secondary {
            background: rgba(187, 222, 251, 0.2);
            color: #bbdefb;
        }
        
        .btn-secondary:hover {
            background: rgba(187, 222, 251, 0.35);
        }
        
        .accordion {
            margin-bottom: 30px;
        }
        
        .accordion-item {
            margin-bottom: 12px;
            border-radius: 16px;
            overflow: hidden;
            border: 1px solid rgba(187, 222, 251, 0.2);
        }
        
        .accordion-header {
            background: rgba(187, 222, 251, 0.1);
            border-radius: 16px;
            padding: 20px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            cursor: pointer;
            transition: all 0.3s ease;
        }
        
        .accordion-header:hover {
            background: rgba(187, 222, 251, 0.15);
            box-shadow: 0 5px 15px rgba(0, 20, 40, 0.2);
        }
        
        .question-number {
            width: 40px;
            height: 40px;
            background: linear-gradient(135deg, #64b5f6, #2196f3);
            border-radius: 12px;
            display: flex;
            align-items: center;
            justify-content: center;
            color: #0a2e4d;
            font-weight: bold;
            font-size: 1.1rem;
            flex-shrink: 0;
        }
        
        .question-text {
            flex: 1;
            padding: 0 20px;
            font-size: 1.1rem;
            font-weight: 600;
            color: #bbdefb;
        }
        
        .accordion-icon {
            width: 36px;
            height: 36px;
            border-radius: 10px;
            display: flex;
            align-items: center;
            justify-content: center;
            background: rgba(187, 222, 251, 0.2);
            color: #bbdefb;
            transition: all 0.3s ease;
        }
        
        .accordion-header.active .accordion-icon {
            background: rgba(100, 181, 246, 0.4);
            color: #64b5f6;
            transform: rotate(180deg);
        }
        
        /* ✅ Smooth expand & collapse — blue theme */
        .accordion-content {
            background: #bbdefb; /* Soft sky blue background for answers */
            border-top: 1px solid rgba(187, 222, 251, 0.4);
            padding: 0 20px;
            overflow: hidden;
            /* Collapsed state */
            max-height: 0;
            opacity: 0;
            visibility: hidden;
            /* Collapse animation: 0.5s */
            transition: 
                max-height 0.5s ease,
                opacity 0.5s ease,
                padding-top 0.5s ease,
                padding-bottom 0.5s ease,
                visibility 0.5s;
            transition-delay: 0s, 0s, 0s, 0s, 0.5s;
        }
        
        .accordion-content.active {
            /* Expanded state */
            max-height: 800px;
            opacity: 1;
            visibility: visible;
            padding: 20px;
            /* Expand animation: 0.7s */
            transition: 
                max-height 0.7s ease,
                opacity 0.7s ease,
                padding 0.7s ease,
                visibility 0s;
        }
        
        .answer {
            display: flex;
            gap: 15px;
        }
        
        .answer-icon {
            color: #1565c0; /* Deep royal blue — crisp and professional */
            font-size: 1.2rem;
            margin-top: 4px;
            flex-shrink: 0;
        }
        
        .answer-text {
            line-height: 1.6;
            color: #0a2e4d; /* Deep navy — high contrast on light blue */
            font-size: 1.05rem;
            flex: 1;
        }
        
        .loading {
            text-align: center;
            padding: 40px 20px;
            font-size: 1.2rem;
            color: #90caf9;
        }
        
        .loading i {
            font-size: 2rem;
            margin-bottom: 15px;
            color: #64b5f6;
            display: block;
        }
        
        .error {
            background: rgba(255, 205, 210, 0.15);
            color: #ffcdd2;
            padding: 20px;
            border-radius: 10px;
            margin: 20px 0;
            text-align: center;
            font-size: 1.1rem;
            border: 1px solid rgba(255, 205, 210, 0.3);
        }
        
        /* Physics equation styling */
        .physics-equation {
            font-family: 'Cambria Math', 'Times New Roman', serif;
            font-size: 1.3em;
            margin: 12px 0;
            padding: 10px 15px;
            background: rgba(10, 46, 77, 0.08);
            border-radius: 6px;
            border-left: 3px solid #1565c0;
            display: inline-block;
            min-width: 80%;
            color: #0a2e4d;
        }
        
        .physics-inline {
            font-family: 'Cambria Math', 'Times New Roman', serif;
            font-style: italic;
            color: #0a2e4d;
        }
        
        sup, sub {
            font-size: 0.8em;
            line-height: 0;
            color: #0a2e4d;
        }
        
        html {
            scroll-behavior: smooth;
        }
        
        .loading-container {
            background: rgba(187, 222, 251, 0.1);
            border-radius: 16px;
            padding: 30px;
            text-align: center;
            margin: 20px 0;
            border: 1px solid rgba(187, 222, 251, 0.2);
        }