The "Start Over" text in the Update diff dialog was floating in

free space below the box. This was due to huge line spacing.

Now the "Start Over" text sits in the bottom right-hand corner of

the dialog box.
Similarly, the contents of the dialog box were off centre and were

touching the border, which looked bad.

Now the contents are centered both vertically and horizontally

which looks much nicer.

These changes were tested in Chrome 47, Firefox 43, and Safari 9

by viewing them in each browser and nothing seemed broken.
The bug could not be reproduced with these changes implemented.