How do I increase font size of headings in Widget?

I’ve found from a previous post on here how to adjust the font size for the text inside a widget

https://www.ads-software.com/support/topic/sidebar-font-size-need-add-setting/

#right-sidebar{
    font-size: 16px;
}

which has resolved that issue, but I’m left with headings that are at a ‘default’ of 13px and I wondered what CSS I would use to increase them to, say 18px.

I’ll look through previous posts on here but in case I’m unsuccessful if anyone can suggest the correct CSS I’d be mightly grateful.

Thanks