LPS-44257 Portal dockbar appears in two lines on mobile devices

Hey @Robert-Frampton,

Here is the update for https://issues.liferay.com/browse/LPS-44257.

As I have already mentioned, the flexbox mixins doesn't work on Firefox 21 and older. I've tried to include the 2009 flexbox syntax in the mixins, but it doesn't work out well. There seem to be some issues with the old syntax working correctly in Firefox, specifically with nested flexboxes where the children of nested flexbox doesn't have the flexibility to grow and shrink. I believe there are workarounds to solve the problem, but it requires some hacks and tricks to get it to work. Since you said we're not going to worry too much about the older firefox versions for now, I'll set this aside and work on it later if necessary.

Please let me know if you have any questions. Thanks!