JSFiddle - React, Tailwind, and code Playground

HTML

<li class="marcacao" onMouseOver="aumenta('html')">HTML5 e CSS3
    <div id="html" class="nivel">100</div>
</li>

<script>
valorInicial = 0;
function aumenta(id){
    setInterval(function(){
    var elemento = document.getElementById(id).innerHTML;//pega o valor da div (no caso numero)
    if(valorInicial <= elemento){
        document.getElementById(id).setAttribute('style', 'width:'+valorInicial+++'%');
    }},20)
}
</script>

CSS

.nivel{
    background-color: red;
    width: 100px;
}