gtk2/demos/widget-factory/widget-factory.css

.small-button {
  padding: 0;
  outline-width: 0;
}

frame.border-inset > border {
  border-style: inset;
}

frame.border-outset > border {
  border-style: outset;
}

frame.border-groove > border {
  border-style: groove;
}

frame.border-ridge > border {
  border-style: ridge;
}

/* These effects use 2 lines, so show them */
frame.border-groove > border,
frame.border-ridge > border {
  border-width: 2px;
}