im looking for a script, runnable from the favorites bar, that when clicked changes a web page appearance, adding like you would manually in inspect a line

what i would like to do is edit a website that is not mine which i can do it with inspect and it works, but if i refresh obviously the content disappears. im looking for a way to let it stay and i think it needs a script that would add the text that would then become content to the html code like yo