Vanilla JS doesn't work

Hi everyone !
I don’t use angularjs and I want to use vanilla JS but it doesn’t work :cold_sweat:
I tried a little and simple code to try and it doesn’t work !

First I have this simple h5 title in my HTML code. The text appears in the app so it’s OK.
<h5 id="h555" class="text-align">Welcome</h5>

I added this little code (that works in CodePen) in a js file (app, service and controller, I tried the three files).
var h555 = document.getElementById('h555'); = '#25ff1f';

The text appears but the color is not set to #25ff1f, I don’t know why :confused:

Sorry for my bad english, it’s not my motherlanguage and I still have to progress :grin:

Thanks a lot everyone ! :grinning: