Hi Nitesh,

Which Platform version are you using, and which theme?
It seems to be a mismatch between the CSS required by the component and the one provided by the theme.

If you are using version 11, I strongly recommend you to use the Ballon widget instead.

Cheers.

Bum... I think the Balloon is for use with OutSystems Ui, not Silk themes. 

Either way, I would avoid this design. It is terrible. 

If you wants to use it anyway, try to limit the max number of items to show and put a link to open in a new page to see full list. 

Or just set a link to open a common modal with the list, instead of a balloon. 

In case this helps anyone else, I was able to solve this issue by simply changing the position property from "fixed" to "absolute". I added the following to my CSS:

div.os-internal-Popup.os-internal-ui-dialog {
    position: absolute;
}