tiny-high-contrast-mode/main.html

<a href="#" onclick="document.body.style.filter = 'invert() contrast(1.5) brightness(1.5)'; document.body.style.background = 'white'; var images = document.getElementsByTagName('img'); for(var i = 0; i < images.length; i++) { images[i].style.filter = 'invert() contrast(0.666) brightness(0.666)'; }" style="display:inline-block; padding: 0.25em 0.5em; background-color: white; position: fixed; top: 10px; left: 10px; z-index: 99999;">High Contrast</a>