A high colour contrast ratio between a text and its background makes said text easier to read for colour blind and partially sighted users.
These attributes are used to give an element it's accessible name. They do the same thing but in different ways.
There are humane, technical, financial, and legal arguments in favour of building accessible websites and applications.
Videos are a useful tool to convey information. How do you make sure they are accessible to everyone?
When navigating from link to link by tab key, a user must always be able to see which element receives focus. Define a clearly visible :focus state in your style sheet to achieve this.