css fix: remove tab bullets in FF, make content move down for different widths

[hasMichaels]

• Added @media tags as tab content didn't move down for different widths which resulted in breaking the developer experience when completing KOANs or when debugging with debugger on right.
• Added list-style-none for the tabs, as Firefox added bullets for the tabs
  Tested: Chrome,FF

[hasMichaels]

To test CSS media widths:

• npm run install; npm run setup; npm run start
• open up local client in chrome or FF (http://localhost:8080)
• resize browser from 2556px width -> 400px width and notice that during the resize the tab content remains beneath the tabs

To test FF bullet points are removed from tabs:

• npm run install; npm run setup; npm run start
• open up local client in firefox (http://localhost:8080)
• notice that tabs do not have a list element bullet in front of them
• resize browser from 2556px width -> 400px width and notice that tabs do not have a list element bullet in front of them

[voter101]

👍 merging.

Thanks for the contribution! :)

Have a nice day.