Hover effect not working

Never tried custom css before, my code isn't working but I don't know where I've gone wrong. The selector is right (it works for grayscale) but the hover effect of the thumbnail floating up a bit on hover isn't working.

any tips?

// image hover effect //
.portfolio-grid-overlay .grid-item .grid-image {

       transition: 0.3s !important;

       &:hover {

      transition: 0.3s !important;

      margin-top: -10px;

    }

  }

@Elysian888 Would it be possible to share your site URL so I can take a look? Thanks!