adjusting image size in css

Hi! I’m really struggling to adjust my image size via CSS.
I was able to call the image & move it (left) with:

#supersized img {
left:100px !important;
}

However, I can’t seem to adjust the dimensions of the image or padding…I’ve tried adding

width: XXpx; height: XXpx

with no success & variations on that as well (size: 0.9)…no dice

Solutions? Cheers!