Update and rename newCSSRule.md to injectCSS.md

snippets/injectCSS.md

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+---
+title: injectCSS
+tags: browser,intermediate
+---
+
+Injects the given css code into the current document
+
+- Use `document.createElement()` to create a new `style` element and set its type to `text/css`.
+- Use `Element.innerText` to set the value to the given css string, `document.head` and `Element.appendChild()` to append the new element to the document head.
+- Return the newly created `style` element.
+
+```js
+const injectCSS = css => {
+  let el = document.createElement('style');
+  el.type = 'text/css';
+  el.innerText = css;
+  document.head.appendChild(el);
+  return el;
+}
+```
+
+```js
+injectCSS('body { background-color: #000 }'); // '<style type="text/css">body { background-color: #000 }</style>'
+```