Buttons, nagivation menus (collapsed ones), the calendar --- but mostly buttons, they used to have hover effects when you hovered over them.
This made for a more intuitive, interactive feeling screens.
Heck, Board's own buttons (the in-line menu at the top) that can't be configured have hover effects.
These were removed in the web version (along with alert blocks and colors for vertical layouts). I'm not sure why so many visual elements are being removed -- they are essential to the tool.
I hope these are back in Version 11.