Mixin doesn't apply to an element, but the box-shadow does

I'm trying to add a box-shadow to an element via mixin, but it doesn't work. When I put the box-shadow into the element, it works just fine, but won't take to the mixin. Maybe I'm missing something small, but according to the guide on FreeCodeCamp, it should work just fine. Any help would be awesome

@mixin project-drop-shadows($offsetX, $offsetY, $color) {
  box-shadow: $offsetX, offsetY, $color;
  -webkit-box-shadow: $offsetX, $offsetY, $color;
  -moz-box-shadow: $offsetX, $offsetY, $color;
}

.project-tile{
 @include project-drop-shadows(5px, 10px, yellow);
  box-shadow: 5px 10px grey;
}