Once upon a time, there was a GUI framework tool called Struts and Springs which made you think about placing things based upon rigid-versus-relative margins/padding. It's still kind of a useful concept.
Anytime you see a spring, it's got a percentage sign somewhere in a stylesheet. A strut is represented by something else more static.
I had originally wrapped the other tabs that made the contents of them stretch to the extra width, but was causing issues with the gcode viewer so took it out. The problem you might be experiencing with the sidebar though might be related to either your browser or Themeify plugin styling. Originally I was seeing the issue that you are showing there, but after tweaking it locks in the width of the page so the elements don't resize lower than a specific width.
So I just tested a couple of the Themeify plugin options and there were no issues with scaling. What browser are you using? Also what's your screen resolution?
I've been using it all day and especially now that I've fixed the themeify issue I love it.
I've tested all of the buttons and have had no issues what so ever. If it were up to me, this would be the default experience for Octoprint.
@Warchildz, I mentioned the tab ordering issue in my original post and just haven't had a chance to go back and figure out why there is an issue. I'll add this to the issue tracker on the repository, thanks for reminding me.