SharePoint O365/ Remove left navigation Panel

I am trying to remove the left panel on a modern SharePoint Site: 

I used this on one page and it worked but does not work on other pages...

<style type="text/css"> .ms-HorizontalNavItems { display: none; } </style>
<style type="text/css">
#spLeftNav {display: none}
</style>

Is there something else I can use for the other pages?

Thanks 

Tom Weber