File java/util/doc-files/coll-index.html contains an inline `<style>` element declaring CSS rules for various elements. These rules do not have any effect on the contents of the page, but cause the navigation links to use bold font as can be seen at the following URL:

https://download.java.net/java/early_access/jdk22/docs/api/java.base/java/util/doc-files/coll-index.html