JavaScript Style Sheets (JSSS) was a stylesheet language technology proposed by Netscape Communications in 1996 to provide facilities for defining the presentation of webpages.
It now remains little more than a historical footnote, with web developers generally unaware of its previous existence.
Using JavaScript code as a stylesheet, JSSS styles individual element by modifying properties of a document.tags object.
On the other hand, since it is written using a complete programming language, stylesheets can include highly complex dynamic calculations and conditional processing.
(In practice, however, this can be achieved using JavaScript to modify the stylesheets applicable to the document at runtime.)