The first principle of web accessibility, Perceivable, is about making sure that all users can detect and understand the information presented on a website. This means that nothing should be invisible to anyone, regardless of their abilities or the technology they use. To achieve this, you need to provide text alternatives for non-text content, such as images, so that screen readers and other assistive technologies can convey the information to users who cannot see the visuals. Captions for videos are also essential, as they allow users who are deaf or hard of hearing to access audio content. Another key aspect is ensuring sufficient color contrast between text and its background, which makes content readable for users with low vision or color blindness.