I have a friend that has retinitis pigmentosa, the only way she can work on the computer is if the application or software program she is working with can be modified to have a black background with white text and the text size should be adjustable if this would be a windows theme it should carry across all software applications including web browsers, not just edge but whichever browser that particular person has chosen.
Like now. if I turn on high contrast I can not see the text I have typed, because the theme does not carry through all aspects of the browser. The background remains white on the page, and also in the message area while the text on the page remains black as well. The entire page need to invert the colors within the browser.
In the Windows 10 October 2018 Update and newer you can increase the size of the text by pressing Windows Logo Key + U to get to Ease of Access and selecting Display. You can then use the Make Text Bigger slider to adjust the size of the text.
The Microsoft Edge team has made a lot of improvements to High Contrast support. If you're using a different browser, we would recommend sharing this feedback with the developers of that application.