Open ja.vm.css and look around line 39, you will find:
.addtocart_button {
-moz-background-clip:border;
-moz-background-inline-policy:continuous;
-moz-background-origin:padding;
background:transparent url(../images/button-addtocart.gif) no-repeat scroll left top;
display:inline;
height:30px;
outline-color:-moz-use-text-color;
outline-style:none;
outline-width:medium;
text-indent:-2000px;
vertical-align:top;
width:90px;
}
Change it to:
.addtocart_button {
-moz-background-clip:border;
-moz-background-inline-policy:continuous;
-moz-background-origin:padding;
background:transparent url(../images/button-addtocart.gif) no-repeat scroll left top;
display:inline;
height:30px;
outline-color:-moz-use-text-color;
outline-style:none;
outline-width:medium;
text-indent:-2000px;
vertical-align:top;
width:141px;
}
Make a backup before making changes 🙂