1. Modified CSS:
.button1 {
background:white !important;
border: 2px solid #4CAF50;
}
.button1:hover {
background:#4CAF50 !important;
border: 2px solid #4CAF50;
color: white !important;
transition-duration: 0.5s;
}
.customHover .x-btn-inner {
color: white !important;
font: italic small-caps bold 12px/30px Georgia, serif;
transition-duration: 0.5s;
}
2. Do not forget
procedure TMainForm.UniFormCreate(Sender: TObject);
begin
UniButton1.JSInterface.JSConfig('overCls', ['customHover'])
end;
3. Result: