Detecting element widh DOM javascript -

my question pretty simple, can't detect element, wanna change backgroundcolor through javascript can't check since tag+class + tag+class... here's code tried:

var 1 = document.getelementsbytagname("div"); var 2 = document.getelementsbyclassname("red"); var 3 = document.getelementsbytagname("h2"); var 4 = document.getelementsbyclassname("title"); one.two three.four.style.backgroundcolor ="#00c497"; 

the format "div.red h2.title". hope me, thanks

if can, use queryselector this:

document.queryselector("div.red h2.title").style.backgroundcolor = "#00c497";

<div>    <h2>don't touch</h2>    </div>  <div class="red">    <h2>don't touch</h2>    <h2 class="title">change</h2>  </div>