Hide a button on a LMS (RiseUp)

Hello everyone !

I have an issue on my code :'(
I want to hide a button but everything i can do for now is to hide the container.
This one is working properly :

let nextmodule = window.top.document.getElementById("mainViewContent");
nextmodule.style.display = "none";

Div with ID "mainViewContent" get (style="display: none;")

 

But i cant reach the 'next' button... i tried by looking for his 'class' : 

let nextmodule = window.top.document.getElementById("mainViewContent").getElementByClassName("btn btn-primary next nav-bottom-next nav-change-step mr-0");

nextmodule.style.display = "none";

But it doesn't work :'(

Thanks for your help