Version 4.0 or +, update of 2018
ReferenceError: GM_addStyle is not defined
You need to create your own GM_addStyle function, like this :
// ==UserScript==
// @name Example
// @description Usercript with GM_addStyle method.
// ==/UserScript==
function GM_addStyle(css) {
const style = document.getElementById("GM_addStyleBy8626") || (function() {
const style = document.createElement('style');
style.type="text/css";
style.id = "GM_addStyleBy8626";
document.head.appendChild(style);
return style;
})();
const sheet = style.sheet;
sheet.insertRule(css, (sheet.rules || sheet.cssRules || []).length);
}
//demo :
GM_addStyle("p { color:red; }");
GM_addStyle("p { text-decoration:underline; }");
document.body.innerHTML = "<p>I used GM_addStyle.</p><pre></pre>";
const sheet = document.getElementById("GM_addStyleBy8626").sheet,
rules = (sheet.rules || sheet.cssRules);
for (let i=0; i<rules.length; i++)
document.querySelector("pre").innerHTML += rules[i].cssText + "\n";DEPRECATED
If GM_addStyle(...) doesn’t work, check if you have @grant GM_addStyle header.
Like this :
// ==UserScript==
// @name Example
// @description See usercript with grant header.
// @grant GM_addStyle
// ==/UserScript==
GM_addStyle("body { color: white; background-color: black; } img { border: 0; }");