chromium/third_party/blink/web_tests/fast/reflections/reflection-masks.html

<img src="resources/kate.png" style="-webkit-box-reflect:below 2px url(resources/vignette-mask.png) 75 75 75 75 stretch stretch">
<img src="resources/kate.png" style="-webkit-box-reflect:below 2px linear-gradient(transparent, transparent 50%, black)">