Not sure I like it, any reason why you want it?

But I got tempted to give it a try with clientonfocus/blur and some selfmade CSS.

Code:
    Object oLoginName is a cWebForm
        Set psLabel to "loginname"
        Set peLabelPosition to lpTop
        Set piMaxLength to 20
        Set piColumnIndex to 1
        Set pbShowLabel to True
//        Set psPlaceHolder to "loginname"
        Set piColumnSpan to 10
        Set psClientOnFocus to 'floatLabel'
        Set psClientOnBlur to 'unfloatLabel'
        Set psCSSClass to 'test-float'
    End_Object
    
    Object oPassword is a cWebForm
        Set psLabel to "Password:"
        Set pbPassword to True
        Set peLabelAlign to alignLeft
        Set piMaxLength to 20
        Set peLabelPosition to lpTop
        Set pbShowLabel to True
//        Set psPlaceHolder to "password"
        Set piColumnSpan to 10
        Set piColumnIndex to 1
        Set psClientOnFocus to 'floatLabel'
        Set psClientOnBlur to 'unfloatLabel'
        Set psCSSClass to 'test-float'
    End_Object
JS
Code:
function floatLabel(oEvent) {
    var oObject = oEvent.oSource._eLbl.classList = 'float';
}




function unfloatLabel(oEvent) {
    var oObject = oEvent.oSource._eLbl.classList = '';
}
CSS
Code:
.WebControl>div>label{
	transform:translate(13px, 40px);
	opacity: 0.5;
}


div.test-float label.float{
	font-size:14px;
	opacity: 1;
	transform: translate(0px, 0px);
	transition: 0.3s;
}
Used webordermobile (login) as a test. It needs some refining, mostly the CSS, but for the login screen it worked.