Hello,
Cosmetic annoyance with 2.9.9.7 HDPI.
The expanders are flush left in the binder panel (see below). The right side does appear to have padding.
FWIW, it is the same for the non-HDPI version. In Options → Apearance → Binder → Binder and Outliner Extra Indent you can increase the space slightly up to 5px, then no more. See screenshot:
Ah! So close 
Unfortunately, the indent appears to be adjusting the padding of the items, rather than the panel!
Yes. And I’ve found no other way to make the adjustment.