Use semantic HTML search element

[thekid]

This pull request wraps the search bar on the home page as well as the search page inside the semantic <search> element. Quoting MDN:

The <search> element semantically identifies the purpose of the element's contents as having search or filtering capabilities

This improves accessibility in browsers supporting this tag.

See also

• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/search
• https://caniuse.com/mdn-html_elements_search
• https://survey.devographics.com/de-DE/survey/state-of-html/2023
• https://stackoverflow.com/questions/37151908/what-happens-to-old-browsers-if-i-use-the-new-html5-tags