Auto dimming rear view mirror

On my 2017 Prius 4, I have the auto dimming rear view mirror which includes Homelink. I set up Homelink and everything works fine. I was driving home in the evening and when I went to press the button to open the garage, the little buttons were not lit on the mirror. The button worked just fine though. Are these buttons suppose to be lit in the evening? I had this same type of mirror on my 2012 Sienna and the buttons were always lit in the evening, so not sure if there is something different with this mirror. Thanks.