Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Aplikacja Dodawanie</title>
    <style>
        body{
            background-color: black;
            color:white;
        }
        .text-center{
            margin:0 auto;
            text-align: center;
            width:100%;
        }
        .btn{
            border:none;
            background-color:gray;
            padding:10px;
            border-radius:25px;
            transition:0.4s;
            outline:none;
        }
        .btn:hover{
            transform:scale(1.1);
        }
        #answer{
            width:10%;
            outline:none;

        }

    </style>
</head>
<body>
    <div class="text-center">
        <p id="mathBlock">
            <span id="firstElem"></span>
            <span>+</span>
            <span id="secElem"></span>
            <span>=</span>
            <span><input type="number" autofocus id="answer"/></span>
        </p>
        <button class="btn"  onclick="check()">Sprawdz!</button>
    </div>
    <script>
        var x=0;
        var y=0;
        function init()
        {
            document.getElementById("answer").style.backgroundColor="white";
            document.getElementById("answer").value="";
            x=parseInt(document.getElementById("firstElem").innerHTML=Math.floor(Math.random() * 10));
            y=parseInt(document.getElementById("secElem").innerHTML=Math.floor(Math.random() * 10));
        }
        function sleep(ms) {
             return new Promise(resolve => setTimeout(resolve, ms));
        }
        function check()
        {
            var ans=parseInt(document.getElementById("answer").value);
            if(x+y==ans){
                document.getElementById("answer").style.backgroundColor="green";
                sleep(1000).then(()=>{
                    init();
                });
            }
            else{
                document.getElementById("answer").style.backgroundColor="red";
                sleep(1000).then(()=>{
                    init();
                });
            }
        }
        init();

    </script>
</body>
</html>