I was able to do something with conditional formatting although it does not highlight the last cell. If there are two in a row, it highlights just the first cell. If there are three in a row, it highlights the first two.

Anyhoo, select the entire range of data. In conditional formatting, go to New Rule, and Use Formula...

Use this formula... =AND(A$2<90,B$2<90)

Set the format you want.