Where can I find User StyleSheets or add a Custom StylSheet

[Daniel_Idem]

I want to change how some html elements are displayed on my browser.

[#2]

@Daniel_Idem 

Get Started With Viewing And Changing CSS - Microsoft Edge Development | Microsoft Docs

[#3]

@Daniel_Idem 

Use an extension. I can recommend Tampermonkey - Microsoft Edge Addons which gives untold opportunities. Otherwise, you can apply a custom style sheet by using a bookmarklet. Here's one with a single style (text-decoration:underline !important) that you can add to at will.