* {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            font-family: 'Microsoft YaHei', sans-serif;
        }
        
        body {
            background: linear-gradient(135deg, #e3f2fd, #bbdefb);
            color: #333;
            padding: 20px;
            min-height: 100vh;
        }
        
        .container {
            max-width: 800px;
            margin: 0 auto;
            background: white;
            border-radius: 15px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.15);
            overflow: hidden;
        }
        
        header {
            background: linear-gradient(90deg, #1e88e5, #0d47a1);
            text-align: center;
            padding: 25px 0;
            color: white;
        }
        
        h1 {
            font-size: 32px;
            margin-bottom: 8px;
        }
        
        .input-section {
            padding: 25px;
            border-bottom: 1px dashed #e0e0e0;
        }
        
        .input-group {
            display: flex;
            align-items: center;
            margin: 15px 0;
            flex-wrap: wrap;
        }
        
        .input-group label {
            width: 140px;
            font-weight: bold;
            color: #1565c0;
        }
        
        .coeff-input {
            width: 70px;
            padding: 10px;
            border: 2px solid #90caf9;
            border-radius: 8px;
            text-align: center;
            margin: 0 8px;
            font-size: 18px;
        }
        
        .equation-display {
            text-align: center;
            font-size: 26px;
            margin: 25px 0;
            padding: 15px;
            background: #f5f9ff;
            border-radius: 10px;
            font-family: 'Cambria Math', serif;
        }
        
        .buttons {
            display: flex;
            gap: 15px;
            margin: 25px 0;
            justify-content: center;
        }
        
        .btn {
            padding: 12px 25px;
            border: none;
            border-radius: 8px;
            color: white;
            font-size: 18px;
            cursor: pointer;
        }
        
        .btn.solve {
            background: linear-gradient(to right, #00c853, #009624);
        }
        
        .btn.reset {
            background: linear-gradient(to right, #ff5252, #d32f2f);
        }
        
        .solution {
            padding: 25px;
            background: #e8f5e9;
        }

        .method-steps {
            background: #fff;
            border-left: 5px solid #4caf50;
            padding: 20px;
            margin: 20px 0;
            border-radius: 0 10px 10px 0;
            font-size: 18px;
            line-height: 1.8;
        }
        
        .step-highlight {
            background: #fffde7;
            padding: 3px 8px;
            border-radius: 5px;
            font-weight: bold;
            color: #f57f17;
        }
        
        .error {
            color: #d32f2f;
            background: #ffebee;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
            border-left: 4px solid #d32f2f;
        }
        
        .footer {
            text-align: center;
            padding: 20px;
            background: #0d47a1;
            color: #e3f2fd;
        }
        
        .selection-info {
            background: #e3f2ff;
            padding: 10px;
            border-radius: 8px;
            margin: 10px 0;
            border-left: 4px solid #2196f3;
        }