Opening the choose widget dialog in Web AppBuilder and selecting a widget does not highlight the widget. If I click ok the last widget I clicked on gets added, however, there is no visible indication that the widget has been selected.
Chrome Version 56.0.2924.87
WAB Version 2.3
Node.js Version 6.10
Mac OS X El Capitan Version 10.11.6
In WAB 2.1 and above the selected widget should get a check box in the upper left corner once selected. Are you saying you do not see that? If so do you have the svg mime type added to your web server?
Although it ended up not being an issue with the SVG MIME type, these links helped me to identify the issue. I opened up the Developer Console and saw these 404 errors:
Original File Path: client/builder/plugins/widget-config/css (<email address>)/images
Update File Path: client/builder/plugins/widget-config/css/images
This temporarily worked; however, the CSS folder name changed back a few minutes later.
I've narrowed down the issue to having my files stored on Box. Apparently there was some type of conflict detected with having 2 CSS folders in the same location. This resulted in Box renaming the CSS folder to CSS (username) which in return broke the folder path structure Web AppBuilder was looking for. I ended up deleting both local and hosted versions of the CSS folder, and then copying back in a fresh version of the folder.