Hello There,
Please use the following CSS instead:
.tp-caption.large_bold_white, .large_bold_white {
-webkit-text-stroke: 1px black;
color: white;
text-shadow: 3px 3px 0 #000, -1px -1px 0 #000, 1px -1px 0 #000, -1px 1px 0 #000, 1px 1px 0 #000;
}
Hope this helps.