Add CSS styling for tables

[IgnaceMaes]

Currently tables are unstyled in the guides. Some CSS should be written for the table element so it looks nicer.

[Ziphozenkosimthombe]

can I take that?

[IgnaceMaes]

Feel free to give it a go!

Some extra details:

• The styleguide should be used for color and spacing variables: https://ember-styleguide.netlify.app/concepts/colors/
• An example of a table should be added to a markdown file in the test app so this can be revieed.
• There is no design ready to follow. I think it would be nice to make the table full width. Try to make it fit in with the rest of the page.

[Ziphozenkosimthombe]

if I ask the table I should add it to the test-app folder inside the readme file? can you please give me more guidance on that.

[ArunPragadeeswar007]

@IgnaceMaes please review this PR