CA Recall Ballot Fraud with Flashlight

I was filling out my ballot to recall Gov. Newsome in California and noticed that if I held a flashlight to the back of the mail-in envelope with my ballot inside, it was very easy to see whether I has voted to recall Newsome or not. Meaning it'd be easy for someone to simply throw out ballots that voted in a way they didn't agree with. This could be something that's a problem with all mail-in ballots in all 50 states. But it's certainly a potentially huge problem in California.