[BUG] Mobile UI: Statvar selector widget doesn't expand '+'

[ajaits]

Describe the bug

The statvar selector widget doesn't expand dropdown on clicking '+' in the mobile UI

To Reproduce

URL: https://datacommons.org/tools/statvar
Browser: Android Chrome

Steps to reproduce the behavior:

1. Go to 'https://datacommons.org/tools/statvar'
2. Click on 'Select Variables'
3. In the pop up window, click on '+' to expand the dropdown list of statvars
4. The drop down doesn't expand to show child group statvars.

Expected behavior

Clicking on '+' should show the child statvars and change level icon to '-'

Screenshots

Additional context

The drop-down doesn't expand even when using 'view as desktop' on mobile.

[pradh]

+10 to this. Since the LHS widget doesn't expand, mobile mode is a hack to see wide SVs on desktop. Might be useful to fix this.