"Accessible" styling isn't very accessible :)

There are 2 aspects of the "Accessible" theme that are not very accessible.
1. The background color of very light yellow on a white page make it incredibly difficult to even tell that this is a slider.
2. There is no keyboard focus indicator if you use the tab key to go to the slider. Any time you set `outline: none;` on an element, you need to find another way to show when the element has focus. Maybe an outline on the thumb, if you don't like the whole slider being outlined.