JS
(quick guide & examples)
CREATE LINK TAG var ss = document.createElement("link"); ss.rel = "stylesheet"; ss.type = "text/css"; ss.href = "STYLE.CSS";
INSERT INTO HEAD document.head.appendChild(ss);
let ss = new CSSStyleSheet(); ss.insertRule("#demo { color: red; font-weight: 700; }"); document.adoptedStyleSheets = [ss];
CSS RULES <style>#demo { color: blue; }</style>
DELETE & INSERT NEW RULE let ss = document.styleSheets[0]; ss.deleteRule(0); ss.insertRule("#demo { color: red; font-weight: 700; }");
DEFINE CSS VARS :root { --demo-color: black; }
JS REPLACE CSS VARS document.documentElement.style.setProperty("--demo-color", "red");
USE CSS VARS #demo { color: var(--demo-color); }