The 4-3 decision in Teigen v. Wisconsin Election Commission is here. From Justice Rebecca Bradley’s opinion for the majority:
We hold the documents are invalid because ballot drop boxes are illegal under Wisconsin statutes. An absentee ballot must be returned by mail or the voter must personally deliver it to the municipal clerk at the clerk’s office or a designated alternate site.
Justice Ann Bradley (joined by Justices Karofsky and Dallet) dissented. The Milwaukee Journal Sentinel has this story, and AP this one.