orlovmax

Transparent 1px image placeholder

<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7">

And black one: 

<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAUEBAAAACwAAAAAAQABAAACAkQBADs=">

orlovmax

Less css trick to generate BEM-styled selectors, by Max Shirsin, http://noteskeeper.ru/1139 + Scss version

@block: ~".dm-import-feed";

@{block} {
    &_step_2 {
        @{block}__page_step_2 {
            display: block;
        }
    }