Why I cannot set property innerhtml of null showing?
<!DOCTYPE html>
<html>
    <head>
        <title>Page Title</title>
        <script>
            var scr1 = 0;
            var scr2 = 0;
document.getElementById("demo").innerHtml= "Paragraph changed!";
document.getElementById("CS").innerHtml = "Your Score :"
function srt() {
 var a = document.getElementById("none");
     a.style.boxShadow = "none"
     setTimeout(function re(){
         a.style.boxShadow = "-4px -4px grey"
     },200)
}
        </script>
    </head>
    <body>
    <h2 class="scr1" id="dome">Your Score :</h1>
    <h2 class="scr2" id="CS">Com Score :</h2>
    <br />
    <br />
    <center>
    <div class="mid"></div>
    <div class="srt" id="none">
        <h4>Start</h4>
    </div>
    </center>
    </body>
</html>
Please help me with this code
Inner HTML not working I can't find where is error so please help me
 
     
     
    