The contribution payment verification page has lost the site theme styling
Do you see &amp;snippet=1 in your contribute page URL?

That parameter can be used to deactivate the theme on a CiviCRM page.

Eg -


CiviCRM demo donate page as per normal &amp; then without theme
CiviCRM profile page as normal &amp; same without theme


If that parameter is present in the link to your contribution page, remove it and see if this restores the proper theme.

Does your contribute page still work without the theme?