Steps to reproduce (assumes ChromeVox or similar)

1. [Tab] or [Shift+Tab] to the color theme picker at the top left of the page
2. Listen to the screen reader

Actual Result

Elastic UI tilde light, button collapsed

Expected Result

"Choose a color theme. Current theme: light, button collapsed"

Here you want to indicate two things:

1. That there is a list here. "button collapsed" implies this, but it should be explicit
2. That the current selected item is "light"

Suggested Fix
Provide more narrated context either by utilizing the simple title attribute.
Category: #615: Elastic UI Chrome Accessibility
Relevant WCAG Criteria: 2.4.4 Link Purpose (In Context)