spfx – SharePoint Framework: How to handle overlapping web parts?

We have two web elements that are supposed to be used together. One can be placed above the other. The upper web part allows you to open a drop-down menu.

The problem: this drop-down opens. under the lower web part. The user can not interact with him:

hidden pull-down

Two possible solutions are:

  • manipulate in some way the z-index of the upper web part to be "higher" than the lower web part
  • expand the height of the top of the web when you open the drop-down menu (although it seems strange)

How is this supposed to be handled in SharePoint Framework? Can I specify the base z-index of a web element? Anything else?