Fix octicon sizing

[dvrylc]

• [X] Bug fix

Fixes #1096.

What is the rationale for this request?

Currently, icons are sized by using CSS classes (fa-2x for example) that set the font-size property. Since octicons are not font-based but rather SVG-based, this style does not affect them, causing them to be incorrectly sized.

What changes did you make? (Give an overview)

This PR sets the height and width for octicons to 1em, allowing them to inherit their parent container's font size as its dimensions.

Testing instructions:

1. Use an octicon where you would expect it to be a different size. Some examples are:
   • Headings
   • Box icon with a custom icon-size
2. The size of the octicon should match where it's used

Credits

• @ang-zeyu for the generalized solution (in the comments below)
• @hcwong for the existing work on Octicons: support icon-size property #1128 (which this PR fixes as well)

Proposed commit message: (wrap lines at 72 characters)

Fix octicon sizing

[ang-zeyu]

How about simply

.octicon {
  width: 1em,
  height: 1em,
}

?

This would allow it to be responsive in any container instead of just headings.
It would likely fix #1128 as well

[dvrylc]

.octicon {
  width: 1em,
  height: 1em,
}

Oh right that makes sense, thanks!