#page-action-buttons > *[class^=urlbar-icon]{
  margin-inline-end: -26px;
  opacity: 0;
  transition: margin-inline-end 200ms linear, opacity 200ms linear;
}
:root[uidensity="compact"] #page-action-buttons > *[class^=urlbar-icon]{ margin-inline-end: -22px; }
#page-action-buttons:hover > *[class^=urlbar-icon],
#page-action-buttons > *[class^=urlbar-icon][open],
#page-action-buttons > *[class^=urlbar-icon][open] ~ *[class^=urlbar-icon]{
  opacity: 1;
  margin-inline-end: 0px !important;
}