Quote from luishp on July 21, 2019, 7:41 pm

1) On a colored page (background different than white),
2) Go to Project > Properties > Styles and paste this code:

.loader {
  background: rgba(0,0,0,0)!important;
  border-radius: 50%;
  border: 1px solid rgba(0,0,0,0)!important;
  border-top: 2px solid #fff!important;
  animation: spinner1 600ms linear infinite;
}
@keyframes spinner1 {
to {
  transform: rotate(360deg);
}

3) Add a Container object to the page (be sure it is perfectly square)
4) Go to the Properties panel > Advanced > CSS-class and choose "loader"

Run :)