If you are using @media print, you need to add !important in your styles, or the page will use the element’s inline styles that have higher priority.
E.g.
<div class="myelement1" style="display:block;">My div has an inline style.</div>
In @media print, add !important and be a winner
@media print {
.myelement1, .myelement2 { display: none !important; }
}