I actually have two questions.
1) First of all, I want to use the triple format( `) instead of this double-quoted code text. I don't remember this exactly, but I found it and replaced the (') with ( 3````). When the user clicked on the code icon,( ```) quotes were added. How do I change this?

2) For example, when I install the contactus plugin. The Contactus text is written with shadow, I change its style from the plugin file, it works and the text becomes shadowless.

But after a while, I saw that these values ​​changed and returned to their previous state. Could this be because I use php flarum cache:clear from the terminal?

I don't really understand what you are trying to do.

If you want to modify an extension, you will have to fork it (make a copy), makes changes, re-compile its javascript and load it through a custom Composer repository. If you modify an extension in the vendor folder, your changes will be lost whenever you perform updates.

For changes that are only visual and can be done with CSS, you probably don't need to modify the extension at all. Just add your additional CSS to the admin panel "Custom CSS" to override the default CSS from the extension.

Even for javascript changes, you might be able to create a new extension that changes the behavior of another extension, that way you can still update the original extension without having to port your customization every time you want to update.

    clarkwinkelmann I am changing the drop shadow effect of the "Contact Us" text in the contact us extension from the extension's own css file. After a while, I see that the part I changed has returned to its previous form. You are telling me to change the extension and then install it. This is a long issue. I can't write extension from scratch. Looks like I have to change in custom css. But character limit is very less in custom css place.

      Nodeloc Yes, when the user clicks once, the codes there are not colorfully written. But when you write the code and use 3'' in those codes, it becomes colorful. Generally I want the codes to appear in color. When you change this from the root file. After some time, that change returns to its previous form. It would be great if there was an extension for this.