Fix UI issues in nuxeo-document-import popup

When try to import multiple documents in nuxeo-document-import-popup, UI is broken.

Steps to reproduce:
1. Go to Workspace and click on the + icon to import documents.
2. Click on Import, select and upload multiple files.
3. Observed that the UI is broken and documents are out of the box.
4. Also click on the Add Properties button. Here also, the list of documents overflows and unable to scroll through the list.

Expected:
1. The UI in the import tab is not breaking, and uploaded documents are present only in dropzone.
2. The list of documents in Add Properties should be in the prescribed box and scrollable.