Please allow #img css to be edited

[smashah]

Just how on paper-card there's
@apply --paper-card-header-image;

Can we please change:

#img {
        display: block;
        width: var(--iron-image-width, auto);
        height: var(--iron-image-height, auto);
      }

to

#img {
        display: block;
        width: var(--iron-image-width, auto);
        height: var(--iron-image-height, auto);
        @apply --iron-image-image;
      }