Steps to replicate the issue (include links if applicable):

• Be a patroller
• Open an unreviewed article
• Drag the toolbar a bit
• Zoom your browser in a lot

What happens?:

• Toolbar goes completely off the screen

What should have happened instead?:

• Toolbar should stay on the screen

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

• The fix is probably to compute the toolbar's x+width and y+height, and make sure that those two coordinates are not outside the viewport's width and height. If it is, adjust the toolbar's x and y
• The toolbar has a way of staying on the screen if it is not dragged before zooming. Perhaps that codepath could be used.