Arrow css style is not working in Firefox for a canvas

Version : Smartgwtpro4.1

Browser version: Firefox 24.7.0

I have applied a css arrow style to canvas..

public class Route extends Canvas {

public Route(boolean isRequest) {
super();
setWidth(75);
setHeight(20);
setLayoutAlign(VerticalAlignment.CENTER);
setStyleName(isRequest ? "right_arrow_box" : "left_arrow_box");
}

}


here is the css :

.right_arrow_box
{ position: relative;
background: #88b7d5;
height: 20px;
border: 2px solid #c2e1f5;
margin-right: 15px;
}
.right_arrow_box:after, .right_arrow_box:before
{ left: 100%;
top: 50%;
border: solid transparent;
content: " ";
height: 0;
width: 0;
position: absolute; pointer-events: none;
}
.right_arrow_box:after
{ border-color: rgba(136, 183, 213, 0);
border-left-color: #88b7d5;
border-width: 13px;
margin-top: -13px;
}
.right_arrow_box:before
{ border-color: rgba(194, 225, 245, 0);
border-left-color: #c2e1f5;
border-width: 16px;
margin-top: -16px;
}

The arrow is not visible in firefox whr as its visible in other browsers.. Please respond