Card button tooltip UI fixes

[mk-fan]

Problem

• Card button tooltip has weird box shadow
• Card button tooltip shows up even when button is disabled

Solution

• Set background of tooltip Overlay to false
• Check if button is disabled in mouseover handler

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mk-fan]

After discussion, we will include the box-shadow fix in a bigger release focusing on theme adjustments.