Accessibility means the design of products in a way that they can be used by people with disabilities. Many projects neglect this issue as any additional effort is seen as an unnecessary cost. Some of these requirements are probably already taken into account in your frontend visual library like bootstrap. But some of these points also improve regular user experience, boost your SEO and help index your website. Accessibility standard used around the world and used as a requirement is usually WCAG 2.0/2.1.