UI issue: Multiple class select on tiles feature from 1.7b1 doesn't scale beyond 15 css classes

[fredvd]

With the introduction of feature #779 The drop down box which used to be a single select is now not a multi-select but a list of checkboxes that is bound by the dimensions. After +/- 15 items depending on your base font size the drop down is cut off by the overlay.

Test with vanilla collective.cover buildout: Vertical scrolling is activated in the overlay bounds, but the mouse pointer changes as well and I cannot select/activate the scroll bar of the overlay. Work around at the moment is the scroll wheel if your mouse has one. Browsers are not consistent though:

• Chrome Mac I cannot use the overlay scroll bar with the mouse but only use scroll wheel
• Firefox Mac The overlay scroll bar is draggable by the mouse, scroll wheel also scrolls internal overlay
• IE 11 Windows 10, overlay scroll bar is draggable by the mouse, scroll wheel scroll overlay but also the background/page.
• Edge Windows 10, behaves the same as IE11 Windows 10
• Chrome Windows 10 is the worst of both: scroll bar is not draggable and scroll wheel moves the backdrop page instead of the overlay. :-(

To avoid all this:

I'd expect the scroll-bar to appear on the dropdown menu itself (like the 'native' select) with a max height of 10-12 items too keep it in side the overlay if that's possible.

[fredvd]

Oh, the problem also exists when you want to change the class on a column or row, there the overlay is much smaller and the issue is more difficult to work around: