JSFiddle - React, Tailwind, and code Playground

HTML

<h1 id=d>111111111111111111111111111111111</h1>

CSS

.m {background: white;}
.n {background: yellow;}
body {background: gray;}

JavaScript

var v = true;
function f(data){
return (v = !v) ? '<span class="n">' + data + '</span>' : '<span class="m">' + data + '</span>';
}

d.innerHTML=d.textContent.replace(/\d/g, f);