Write valid and semantic HTML. Write CSS that defines styles that are accessible but also allow user control over the presentation of a webpage.
Structure is everything when presenting content through assistive technology. Valid and semantic HTML make the organization of the content presentable in a meaningful way. CSS, written for accessibility, makes a website’s content easier to consume for everyone. Proper CSS can also be used to provide extra information for screen readers that is not visible on the webpage.
Use the WCAG links provided to get detailed guidelines on how to achieve accessibility for this scenario.