Hi Yu Qiao,
Thank you for contacting Syncfusion support.
We have checked and we are able to reproduce the reported “Container is not displayed fully for the Popup” issue from our side. We have logged the bug report for the same. We will fix this issue and include the issue fix in our upcoming Volume 4 SP1 release which is scheduled to be rolled out by the end of January 2019. We appreciate your patience until then.
Subburaj Pandian V