HTML CSS Buttons Hover Wont Work Through Class

[DebsW]

I don't understand why does this work :\[code\].button:active { position:relative; top: 2px; left:2px;}\[/code\]But this wont work :\[code\].button:hover { font-size:17px;}\[/code\]It works when I use id but I want it to activate for all buttons :\[code\]#btnhome:hover{ font-size:17px;}\[/code\]This works fine but with class it wont? What am I doing wrong?