[Code snippets] Enhance the styling

[thyhmdo]

Example: https://carbondesignsystem.com/contributing/documentation/#usage-template:-for-components-with-one-variant

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Intention

As a doc contributor, it's hard to read the text when it gets cut off. It would be helpful to see this code snippet better in terms of:

• better color-wise
• wrapping the text (so that it doesn't run on and get cut off)

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A few things to consider for this work

• This work only needs to add some CSS, but we need to decide if we want to override just for this page, or all code snippets (Alison)
• Among designers, we would have to provide an ideal stylized specs for how this looks.