* {
            box-sizing: border-box;
        }
        
        body {
            font-family: Arial, sans-serif;
            touch-action: manipulation;
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            margin: 0;
            padding: 10px;
            background: linear-gradient(135deg, #007FAE  0%, #4B9CD3 100%);
        }
        
        .container {
            background: white;
            padding: 15px;
            border-radius: 15px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
            text-align: center;
            width: 100%;
            max-width: 700px;
        }
        
        h1 {
            color: #333;
            margin: 0 0 15px 0;
            font-size: clamp(20px, 5vw, 28px);
        }
        
        .new-problem-btn {
            width: clamp(135px, 12vw, 55px);
            height: clamp(45px, 12vw, 55px);
            padding: 0;
            border-radius: 10px;
            font-size: clamp(16px, 4vw, 20px);
        }
        
        .numbers {
            display: flex;
            gap: clamp(8px, 3vw, 20px);
            justify-content: center;
            align-items: center;
            margin: 15px 0;
            flex-wrap: wrap;
        }
        
        .plus-sign, .minus-sign, .multiplication-sign, .division-sign, .equals-sign {
            font-size: clamp(24px, 6vw, 36px);
            font-weight: bold;
            color: #007FAE ;
        }
        
        .main-content {
            display: flex;
            gap: 20px;
            align-items: flex-start;
            justify-content: center;
        }
        
        .left-section {
            display: flex;
            flex-direction: column;
            align-items: center;
        }
        
        .right-section {
            text-align: left;
            flex: 1;
            min-width: 0;
        }
        
        .feedback {
            font-size: clamp(24px, 5vw, 36px);
            font-weight: bold;
            min-height: 50px;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            margin: 0 0 15px 0;
        }
        
        .time-display {
            font-size: clamp(16px, 4vw, 24px);
            margin-top: 5px;
        }
        
        .correct {
            color: #10b981;
        }
        
        .incorrect {
            color: #000000;
        }
        
        .number-box {
            width: clamp(50px, 15vw, 80px);
            height: clamp(50px, 15vw, 80px);
            background: linear-gradient(135deg, #007FAE  0%, #4B9CD3 100%);
            color: white;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: clamp(24px, 6vw, 36px);
            font-weight: bold;
            border-radius: 10px;
            box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
        }
        
        button {
            background: linear-gradient(135deg, #007FAE  0%, #4B9CD3 100%);
            color: white;
            border: none;
            padding: 10px 20px;
            font-size: 14px;
            border-radius: 25px;
            cursor: pointer;
            transition: transform 0.2s;
        }
        
        button:hover {
            transform: scale(1.05);
        }
        
        button:active {
            transform: scale(0.95);
        }
        
        .button-rows {
            margin: 10px 0;
        }
        
        .button-row {
            display: flex;
            gap: 8px;
            justify-content: center;
            margin-bottom: 8px;
        }
        
        .number-btn {
            width: clamp(45px, 12vw, 55px);
            height: clamp(45px, 12vw, 55px);
            padding: 0;
            border-radius: 10px;
            font-size: clamp(16px, 4vw, 20px);
        }
        
        .stats {
            color: #333;
        }
        
        .stats h3 {
            margin: 0 0 8px 0;
            color: #007FAE ;
            font-size: clamp(14px, 3.5vw, 18px);
        }
        
        .stat-item {
            margin: 5px 0;
            font-size: clamp(12px, 3vw, 16px);
        }

        .stat-rows {
            margin: 10px 0;
        }
        
        .stat-row {
            display: flex;
            gap: 8px;
            justify-content: left;
            margin-bottom: 8px;        }
        
        .number-stats {
            margin-top: 15px;
            padding-top: 15px;
            border-top: 2px solid #e5e7eb;
            color: #333;
            overflow-x: auto;
        }
        
        .number-stats h3 {
            color: #007FAE ;
            margin-bottom: 10px;
            font-size: clamp(14px, 3.5vw, 18px);
        }
        
        .number-grid {
            display: grid;
            grid-template-columns: auto repeat(3, 1fr);
            gap: 3px;
            margin-top: 10px;
            font-size: clamp(10px, 2.5vw, 14px);
            min-width: 350px;
        }
        
        .grid-header {
            font-weight: bold;
            text-align: center;
            padding: 4px 2px;
            background: #f3f4f6;
        }
        
        .grid-cell {
            text-align: center;
            padding: 4px 2px;
            background: #f9fafb;
            border-radius: 3px;
        }
        
        .grid-label {
            font-weight: bold;
            padding: 4px 2px;
            text-align: right;
            white-space: nowrap;
        }
        
        /* Mobile styles */
        @media (max-width: 500px) {
            .main-content {
                flex-direction: column;
                align-items: center;
            }
            
            .right-section {
                text-align: center;
                width: 100%;
            }
            
            .stat-row {
                justify-content: center;
            }
            
            .stats {
                padding-top: 15px;
                border-top: 2px solid #e5e7eb;
            }
        }