How to replace CSS key with matching criteria? No class or ID reference

How to replace CSS key with matching criteria? No class or ID reference

Assume I want to replace all CSS keys

  1. line-height: 24px;

in all CSS rules (for unknown classes or IDs) by the following key

  1. line-height: 20px;

resp. (if necessary):

  1. line-height: 20px !important;

How can I achieve this with jQuery?

The following seems not to work:

  1. $("['line-height=24px;']".css("line-height","20px !important;");

How can I achieve this otherwise?