private void ripple(final int x, final int y) {
        final Element ripple = DOM.createDiv();
        ripple.setClassName("ripple");
        ripple.getStyle().setLeft(x, Unit.PX);
        ripple.getStyle().setTop(y, Unit.PX);
        rippleContainer.appendChild(ripple);
        new Timer() {
            @Override
            public void run() {
                rippleContainer.removeChild(ripple);
            }
        }.schedule(1000);
    }
Gets the mouse y-position relative to a given element.

@param target the element whose coordinate system is to be used
@return the relative y-position
stroom-core-client-widget/src/main/java/stroom/widget/button/client/Button.java