Answer
- Create a round cornered rectangle (white in this case).
- Go to
Effect > Blur > Gaussian Blur...
and apply some blur (you can also do this viafx
in the appearance palette). - Reduce the opacity of the blurred rectangle (you can do this in the appearance panel or the transparency panel).
The exact parameters and values will require some experimentation.
Attribution
Source : Link , Question Author : veighcait , Answer Author : Westside