add a method to remove style property

I think it's not bad to introduce removeProperty() method :)

Author: Fardin

2-ui/1-document/08-styles-and-classes/article.md

@@ -128,6 +128,14 @@ setTimeout(() => document.body.style.display = "", 1000); // back to normal
 
 If we set `style.display` to an empty string, then the browser applies CSS classes and its built-in styles normally, as if there were no such `style.display` property at all.
 
+Also there is a special method for that, `elem.style.removeProperty('style property')`. So, We can remove a property like this:
+
+```js run
+document.body.style.background = 'red'; //set background to red
+
+setTimeout(() => document.body.style.removeProperty('background')); // remove background after 1 second
+```
+
 ````smart header="Full rewrite with `style.cssText`"
 Normally, we use `style.*` to assign individual style properties. We can't set the full style like `div.style="color: red; width: 100px"`, because `div.style` is an object, and it's read-only.