feat(web-view): use `--vscode-editor-font-size` variable

[ShaunSHamilton]

Closes: https://github.com/freeCodeCamp/CodeAlly-CodeRoad-freeCodeCamp/issues/56

Uses the --vscode-editor-font-size css variable so that the editor.fontSize property in settings.json can increase the font-size of the markdown.

I was in the neighbourhood, and decided to contribute

Note: There are other variables you might want to consider adding as well.

Image

Signed-off-by: Shaun Hamilton [email protected]