The others likely all have their own unique rules and selectors. Use your browser’s element inspector tool to learn what rules are applied to any selected element. Look for the applicable property in each case. font-size: in this case (and perhaps other font properties). Test out different values in the tool by directly editing the values. The page will then be updated to reflect the edit. Changes in the tool do not persist, reloading the page reverts back to the original rules.
The properties in the tool are presented in the proper syntax. Once you have determined what appearance you like, for the most part you can copy/paste the altered rules into Additional CSS, removing any properties that you hadn’t changed. One exception being the media queries. They will need slight editing to maintain proper syntax.
The tool is a good learning mechanism. When you add an entirely new rule, it’ll suggest appropriate selectors for the current element. Selectors will often need modification, but the suggestions are always a good start. When you add new properties, once you start typing, the tool will auto-suggest complete properties and values which you can select from. This is useful when you’re not sure what the correct property name was supposed to be. You can guess at the first few letters and auto-suggest will help you out.
The tool’s UI naturally involve a slight learning curve. It’s well worth your time getting to know your way around it. The most useful elements are the element selector, the toggle between mobile and desktop view, the add new rule icon, and how to emulate a hover state without actually hovering on the page, thus freeing your cursor for other usage.
