fix(ui): change escaping button bg on selected lines (#7944)

* add escape part of line to the list of selectors, so it doesn't cause a hole in selected lines
* fix duplicated element ID in template
* move some CSS out of base.css to dedicated files, so it is less cluttered

Before: https://codeberg.org/attachments/0eaa277b-98e7-42de-98a2-6aca99ffcbe4

After: https://codeberg.org/attachments/124bbb86-c377-4fef-a0e3-403e8c850275

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7944
Reviewed-by: floss4good <floss4good@noreply.codeberg.org>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>

web_src/css/markup/content.css

@@ -561,6 +561,10 @@
   border-top-right-radius: 0 !important;
 }
 
+.file-view.markup {
+  padding: 2em;
+}
+
 .file-view.markup.orgmode li.unchecked::before {
   content: "[ ] ";
 }