Chrome Extension Highlighting as Vertical Bars

[sdzhong]

What product do you want to improve? browser extension https://docs.codecov.com/docs/the-codecov-browser-extension

Is your feature request related to a problem? Please describe. The highlighting is too similar to GitHub diff, which makes it hard to interpret/use

Describe the solution you'd like Use of vertical bars on the left-side by the line numbers, e.g.

Describe alternatives you've considered N/A

Additional context N/A

[drazisil-codecov]

@codecovdesign