Fix background corner size, radius and PC3 ToolTip style
The sides and corners now have correct sizes relative to each other. Before, some of the corners were actually larger than sides, which caused weird corner glitches like this:
The corner radii are now consistent and all corners are perfectly semicircular. In some cases they were only semi-semicircular, meaning they had nodes with handles dragged to positions that were close to making corners look semicircular.
PC3 ToolTip now uses a style like normal tooltips.
Fixed tooltip corners and style:
Corner radii differences are hard to see, but they're now the same as everything else.