this is just css, probably is just browser cache not clean. However your test page website at this date does not have a .offst class
and your main site has you said has a inline css and also an id of formulier.
Once this page doesnt have the .offst class, why dont you add an id #my_h2_formulier to that h2 on the test page, and then remove the span on the main with inline css and also add the id #my_h2_formulier to that same h2.
Now just give the css to the #my_h2_formulier instead of the inexistent .offst class in both sites.
One more thing in your development website, you already have a div with an id formulier, and in the main website the div doesnt have that id, instead you have that id in a span.
what can be also causing this issues is that in that page your html isnt the same in both websites. that is probably the biggest issue.