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>

tests/e2e/declare_repos_test.go

@@ -53,6 +53,10 @@ func DeclareGitRepos(t *testing.T) func() {
 				CommitMsg: "Another commit which mentions @user1 in the title\nand @user2 in the text",
 			},
 		}),
+		newRepo(t, 2, "unicode-escaping", []FileChanges{{
+			Filename: "a-file",
+			Versions: []string{"{a}{а}"},
+		}}),
 		// add your repo declarations here
 	}