I tried in Incognito mode so I sure it not the issue.
Moreover , some interesting behavior I found:
In the site’s Theme management menus , when I opening the Theme management page in desktop mode the gap width disappear after I added the CSS code, but when I press on mobile or tablet view the gap backing again and stay although I pressing on desktop mode view button and backing to desktop view. Only after refreshing (F5) the Theme management page in the desktop view the gap disappearing again and so on..