A link checker showed up the following problems:

 grep -r -F ../../stylesheet open/src
open/src/java.base/share/classes/java/lang/doc-files/ValueBased.html: <link rel="stylesheet" type="text/css" href="../../../stylesheet.css" title="Style">
open/src/java.base/share/classes/java/lang/doc-files/threadPrimitiveDeprecation.html: <link rel="stylesheet" type="text/css" href="../../../stylesheet.css" title="Style">

Both of these references need an extra ../
In other contextx, I would recommend using {@docRoot} instead of `../..`
but these are simple .html files that are copied across without interpretation.