Docs: Standardize `custom styles` examples

[joasmi723]

Currently, we have a variety of custom styles examples in our docs, many of them very visually non-appealing. We should create and implement a more consistent and aesthetically attractive way of showing examples of custom styles throughout our docs examples.

Notes: Some components have a section in the docs where we explain that you can customize the styles, like here: https://react-magma.cengage.com/version/2.5.10/api/input/#custom_styles. We need a way to sort of standardize how we show those so they’re still attractive, but very clearly custom.