The stylesheet here shows just the portion which is needed to make the button. A stylesheet is simply a text file with the extension ".css". 

.btnMedium {
	cursor:hand;
	font-family:Verdana,"MS Sans Serif",Charcoal,Chicago,Arial;
	font-weight:bold;
	font-size:big;
	background-color:"blue";
      color:"lime";
      width:200;
}
This text file should be saved as MyStyleSheet.css in the same directory with your page. (Yes, it can be elsewhere, but you will need to correct the link in your heading.)
Note that it starts with .btnMedium. That is its name, and you remember that it is also on the form at each button. There it is part of an attribute written as: 

CLASS="MyStyleSheet.css"