As discussed in this openjfx-dev email thread, there are some inefficiencies in process CSS stylesheets:

https://mail.openjdk.java.net/pipermail/openjfx-dev/2021-March/029303.html

Whenever a stylesheet is processed, it is reread from the provided URL. A checksum is generated to see if it need to be reprocessed, but even the act of reading the HTTPS stream or a File is overhead that may be able to be avoided if we checked the HTTP header or File timestamp as suggested by Richard Bair in this response:

https://mail.openjdk.java.net/pipermail/openjfx-dev/2021-March/029311.html