Transclusion means that .a in this can escape the Shadow DOM: <my-element><div class="a">Transcluded content</div></my-element>

To do the same thing in CSS you would do <div class="myelement"><div class="slot"><div class="a">Transcluded content</div></div></div> @scope (.myelement) to (.slot) { /* rules that apply to .myelement but not .a */ }).