RemixIconEx.System.checkbox_indeterminate

You're seeing just the function checkbox_indeterminate, go back to RemixIconEx.System module for more information.
Link to this function

checkbox_indeterminate(icon_css_class \\ "icon")

iex> Elixir.RemixIconEx.System.checkbox_indeterminate()
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" class="icon">
  <path d="M4 3h16a1 1 0 0 1 1 1v16a1 1 0 0 1-1 1H4a1 1 0 0 1-1-1V4a1 1 0 0 1 1-1zm1 2v14h14V5H5zm2 6h10v2H7v-2z" />
</svg>

example usage

svg.icon {
  width: 96;
  height: 96;
}