Include Alternative Fonts: Arimo, Liberation Sans, Nimbus Sans L and Selawik

[reinhart1010]

This is originally suggested as a workaround for Bug #43, where the devs may use either macOS or Windows styles to make some Linux webapps.
To prevent default Linux font to be used, which may cause metric problems in user interface, I would suggest to include some alternative fonts which are most likely to be available in Linux distros (except Arimo and Selawik, which is available in Google Fonts and Microsoft's GitHub repo respectively).

[gabrielbull]

Sorry for the late reply, but if someone is willing to submit a PR, I'd be happy to accept it.

[reinhart1010]

In addition, here's what the font stack might be

Based on similarity with Arial and Helvetica (good for using macOS application styles)

font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue", HelveticaNeue, Roboto, "TeX Gyre Heros", TeXGyreHeros, FreeSans, "Nimbus Sans L", "Liberation Sans", Arimo, Helvetica, Arial, sans-serif;

Based on http://www.grputland.com/2013/11/multiplatform-helvetica-like-font-stack.html with few additions.

Here's a breakdown of this font stack:

• Mac OS X 10.11 "El Capitan" and above will use San Fransisco system font.
• Mac OS X 10.10 "Yosemite" will use Helvetica Neue system font.
• Here, Roboto is prioritised as it offers multiple weights and similarity to Apple's San Fransisco font. Roboto will be used when the app includes its webfont or Windows and Linux users installed this font to their computers.
• Helvetica lookalikes, i.e. TeX Gyre Heros, GNU FreeSans and Nimbus Sans L are common to Linux users, but only have 2 styles: regular and bold. These fonts will be used when one of their webfonts are included or installed to computers, and in most Linux users.
• Liberation Sans and Arial are designed as alternatives to Arial, which Liberation Sans are common to LibreOffice, an open-source office suite. However, Arimo is common to Google's Chrome OS (alongside Roboto).
• Older versions of Mac OS X will use Helvetica. I do not recommend Lucida Grande (system font) as their metrics do not match with Apple's San Fransisco and Helvetica Neue.
• At last, Windows users will use Arial.