What is Cypress?
Cypress is an open-source Cascading Style Sheet (CSS) parser
  that lets you add 
  well-documented, standardized name/value pairs 
(such as color: red; font-size: 150%; font-style: italic;)
 also know as CSS style properties to your own XML markup languages.
Cypress supports
 inline styles so you can add style properties 
to individual XML tags using the style attribute
 or external style sheets so that you can store style rules for reuse 
in separate, XML-free text documents also known as style sheets. 
Cypress supports three forms of selectors to match your XML tags and style rules,
that is, element selectors, class selectors and id selectors.
  
 
  
What is CSS (Cascading Style Sheets)?
Cascading Style Sheet (CSS) started as a W3C standard 
for styling web pages (that is, HTML tags) and evolved into a 
standard for styling arbitrary, made-up, not-yet-invented XML tags such 
  as XUL or SVG tags. 
Note, that CSS is not and archaic pre-XML-world dialect that is 
endangered by XSL/T. Instead both CSS and XSL/T will thrive 
side-by-side and complement each other. XSL/T, for example, excels 
in creating new documents from templates and XML data, 
but doesn't offer well-documented, standardized style properties 
that you can squeeze into XML tags and that are possibly cascaded/inherited 
to leafs and branches in the document tree.
To find out more about CSS check these links: