top up bootstrap 3 theme for button press down feeling.

bootstrap3_button.css

.btn:active,
.btn.active {
  padding-top: 7px;
  padding-bottom: 5px;
}

.btn-lg:active,
.btn-lg.active {
  padding-top: 11px;
  padding-bottom: 9px;
}

.btn-sm:active,
.btn-sm.active {
  padding-top: 6px;
  padding-bottom: 4px;
}

.btn-xs:active,
.btn-xs.active {
  padding-top: 2px;
  padding-bottom: 0;
}