CSS Masking: Basic shape without a geometry-box should default to stroke-box
The spec states: "If no reference box is specified, the
border-box will be used as reference box", and "For SVG elements without
an associated CSS layout box, the used value for ... border-box and margin-box
is stroke-box." In this testcase, no reference box is specified, so the
clip-path of "inset(0)" should be equivalent to "inset(0) stroke-box", and
should not clip out the stroke. You should see a 100x100 green square formed
by a stroked rect.