RemixIconEx.System.checkbox

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

checkbox(icon_css_class \\ "icon")

iex> Elixir.RemixIconEx.System.checkbox()
<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 2v14h14V5H5zm6.003 11L6.76 11.757l1.414-1.414 2.829 2.829 5.656-5.657 1.415 1.414L11.003 16z" />
</svg>

example usage

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