Reduce code element border radius and add padding

[Staudey]

Description

This reduces the border radius for code elements and slightly increases horizontal padding. The default rounding looks too extreme in my eyes, and makes it feel like the characters are not properly contained, especially with big vertical characters at the start or end of the element.

Before:

After:

Note: Personally I'm somewhat partial to a completely angular style for these elements, but this might be too extreme and/or not fit in with the rest of the theming

0 border radius:

It also looks more consistent across line breaks (which are not ideal in any case, but that's a different topic)

[Staudey]

Actually now that I've prepared the PR the default no longer looks that bad to me, which it always has in the past. Maybe I need to rest my eyes for a while and look at it again.

[davidjharder]

How do you feel with fresher eyes?

[Staudey]

Yeah, I'm back to feeling the default is kinda meh. It seems especially bad to my eyes with the light theme. I could maybe do without the additional padding, but the border radius just feels off. Comments welcome.