editing size of h4 doesn't work :(

hello all,

this should be a rather easy question…
i want to change the size of h4 but it doesen’t work. neither via typography -> text headers nor via custom css. i do manage to change the color though, but font-size changes do not apply.

it concerns the widget titles i have in the right sidebar, i want them to have the same look as the post titles.
is there a possibility that i can set h4 = h1 somehow via css?

or any suggestions?

thank you so much!
hhh.