There is a nice guide in the documentation here:
Basically you can find what you need in the theme\native\custom-variables.js file. Copy what you need from there and use it to create your own styling in a new file. I think it's probably only the padding that you want changed?
you can “inspect” the element on a web browser (even this is a native). And inspecting you can check what file and class you need to change or override.