Please fix color contrast issues in the demo

[mgifford]

Describe the bug
The demo page should be check for color contrast and have accessibility issues fixed.

To Reproduce
If you go here joshuajohnson.co.uk/choices/

Run https://wave.webaim.org/ on it and you see a great many contrast errors because of the painful choice of colors.

Expected behavior
There should be clear and readable. Should comply with https://webaim.org/articles/contrast/

Screenshots

[Xon]

I've picked #005F75 to replace #00bcd4, which provides a good contrast against white according to; https://dequeuniversity.com/rules/axe/4.9/color-contrast.

Added to the list of things to be merged into the big v11.0.0 update I've been working on