froelofs2015

try adding this to your css:

.su-spoiler.my-custom-spoiler .su-spoiler-title, .su-spoiler-icon {
  font-weight: bold;
}
.su-spoiler.su-spoiler-closed.my-custom-poiler .su-spoiler-title, .su-spoiler-icon {
  font-weight: normal;
}

don’t forget to add the class my-custom-spoiler to your spoilers