* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        body {
            background: linear-gradient(135deg, #1a2a6c, #b21f1f, #fdbb2d);
            color: #333;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
        }
        
        header {
            background: rgba(255, 255, 255, 0.9);
            box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
            padding: 1rem 5%;
            display: flex;
            align-items: center;
            position: sticky;
            top: 0;
            z-index: 100;
        }
        
        .logo-container {
            display: flex;
            align-items: center;
            gap: 15px;
        }
        
        .logo {
            width: 60px;
            height: 60px;
            background: linear-gradient(135deg, #1a2a6c, #b21f1f);
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-weight: bold;
            font-size: 28px;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
        }
        
        .logo-text {
            font-size: 1.8rem;
            font-weight: 700;
            color: #1a2a6c;
            text-shadow: 1px 1px 3px rgba(0, 0, 0, 0.1);
        }
        
        main {
            flex: 1;
            padding: 2rem 5%;
            max-width: 1400px;
            margin: 0 auto;
            width: 100%;
        }
        
        .intro {
            background: rgba(255, 255, 255, 0.92);
            border-radius: 15px;
            padding: 2rem;
            margin-bottom: 2rem;
            box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
        }
        
        .intro h1 {
            color: #1a2a6c;
            margin-bottom: 1rem;
            font-size: 2.2rem;
            text-align: center;
        }
        
        .intro p {
            line-height: 1.8;
            font-size: 1.1rem;
            margin-bottom: 1.5rem;
            color: #444;
        }
        
        .theorem {
            background: #e3f2fd;
            border-left: 5px solid #2196f3;
            padding: 1.2rem;
            border-radius: 0 8px 8px 0;
            margin: 1.5rem 0;
            font-size: 1.2rem;
        }
        
        .content-container {
            display: flex;
            flex-wrap: wrap;
            gap: 2rem;
        }
        
        .demo-container {
            flex: 1;
            min-width: 300px;
            background: white;
            border-radius: 15px;
            padding: 1.5rem;
            box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
        }
        
        .controls {
            flex: 0 0 300px;
            background: white;
            border-radius: 15px;
            padding: 1.5rem;
            box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
        }
        
        .demo-container h2, .controls h2 {
            color: #1a2a6c;
            margin-bottom: 1.5rem;
            padding-bottom: 0.5rem;
            border-bottom: 2px solid #fdbb2d;
            font-size: 1.6rem;
        }
        
        #triangle-container {
            width: 100%;
            height: 400px;
            background: #f8f9fa;
            border-radius: 10px;
            position: relative;
            overflow: hidden;
            margin-bottom: 1.5rem;
            border: 1px solid #ddd;
        }
        
        #triangle-svg {
            width: 100%;
            height: 100%;
        }
        
        .vertex {
            cursor: move;
            transition: r 0.2s;
        }
        
        .vertex:hover {
            r: 10;
        }
        
        .angle-display {
            font-size: 1.2rem;
            margin: 1rem 0;
            padding: 1rem;
            background: #f1f8e9;
            border-radius: 8px;
        }
        
        .angle-display span {
            font-weight: bold;
            color: #1a2a6c;
        }
        
        .sum-display {
            font-size: 1.4rem;
            font-weight: bold;
            text-align: center;
            padding: 1.2rem;
            background: #e8f5e9;
            border-radius: 8px;
            color: #2e7d32;
            margin: 1.5rem 0;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
        }
        
        .btn-group {
            display: flex;
            flex-wrap: wrap;
            gap: 1rem;
            margin: 1.5rem 0;
        }
        
        button {
            flex: 1;
            min-width: 120px;
            padding: 0.8rem;
            border: none;
            border-radius: 8px;
            background: linear-gradient(to right, #1a2a6c, #b21f1f);
            color: white;
            font-weight: bold;
            cursor: pointer;
            transition: all 0.3s;
            font-size: 1rem;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
        }
        
        button:hover {
            transform: translateY(-3px);
            box-shadow: 0 6px 12px rgba(0, 0, 0, 0.25);
        }
        
        button:active {
            transform: translateY(1px);
        }
        
        button:disabled {
            background: linear-gradient(to right, #6c757d, #adb5bd);
            cursor: not-allowed;
            transform: none;
            box-shadow: none;
        }
        
        .proof-section {
            background: rgba(255, 255, 255, 0.92);
            border-radius: 15px;
            padding: 2rem;
            margin-top: 2rem;
            box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
        }
        
        .proof-section h2 {
            color: #1a2a6c;
            margin-bottom: 1.5rem;
            font-size: 1.8rem;
            text-align: center;
        }
        
        .proof-steps {
            display: flex;
            flex-wrap: wrap;
            gap: 1.5rem;
            justify-content: center;
        }
        
        .proof-step {
            flex: 1;
            min-width: 250px;
            background: #e3f2fd;
            padding: 1.5rem;
            border-radius: 10px;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
        }
        
        .proof-step h3 {
            color: #1a2a6c;
            margin-bottom: 1rem;
            display: flex;
            align-items: center;
            gap: 10px;
        }
        
        .step-number {
            background: #1a2a6c;
            color: white;
            width: 30px;
            height: 30px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: bold;
        }
        
        footer {
            background: rgba(0, 0, 0, 0.8);
            color: white;
            text-align: center;
            padding: 1.5rem;
            margin-top: 2rem;
            font-size: 1rem;
        }
        
        @media (max-width: 768px) {
            .content-container {
                flex-direction: column;
            }
            
            .controls {
                flex: 1;
            }
            
            .intro h1 {
                font-size: 1.8rem;
            }
            
            .logo-text {
                font-size: 1.5rem;
            }
            
            .logo {
                width: 50px;
                height: 50px;
                font-size: 24px;
            }
        }
        
        @media (max-width: 480px) {
            .btn-group {
                flex-direction: column;
            }
            
            .intro, .demo-container, .controls, .proof-section {
                padding: 1.2rem;
            }
            
            .logo-text {
                font-size: 1.3rem;
            }
            
            .logo {
                width: 40px;
                height: 40px;
                font-size: 20px;
            }
        }