Accessing WebView response after loaded


I’m wanting to inject custom css/js into a <webview> after it loads. I’ve seen the option to [preload] ( a script to execute before other scripts on the page, but what about executing after? I’m basically wanting to be able to hide certain elements of a page from view (I’ve also seen the mention of IPC, but I’ve not been able to digest exactly how that can edit a <webview>'s content). Is this not an issue if the script is loaded beforehand? Thanks!