Some explanations:<p>- this is a companion to previously announced XT.js, but for dynamic CSS construction;<p>- ES5 compatible;<p>- no at-rule support at this point (as we are on JS, .matchMedia FTW, and dynamic @keyframes building is too specific task to multiply the size twice and more);<p>- due to engine limitations we have to already insert the <style> element into <head> before we can even start appending rules, so, unlike XT.js, a reference to already inserted <style> is returned.