Borderless for link

I have created a button with style as BaseTheme.Button_link .I want to remove the border when mouse over the image.Below is the change i did in css

Java Code to create button

Button topBut=new Button();
topBut.setIcon(Icons.topBar);
topBut.setEnabled(false);
topBut.setStyleName(BaseTheme.BUTTON_LINK);
topBut.addStyleName(“borderless”);

//css

.v-button-link-borderless:hover .v-button-link-borderless:focus {
border: none;
outline:none;

}

Can anyone help me on this issue