All Octicons
square-fill
Octicon sizes navigation
React
import {SquareFillIcon} from '@primer/octicons-react' <SquareFillIcon size={24} />
Rails
<%= render(Primer::Beta::Octicon.new(:"square-fill", size: :medium)) %>
Jekyll
{% octicon square-fill height:24 %}
Figma
This icon is called square-fill-24
in Primer's Octicons library.