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(){
v=!v;
return (v)?'<span class=n>$1</span>':'<span class=m>$1</span>';
}

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