In the resize-observer-text.html (see source) example, we use the resize observer to change the font-size of a header and paragraph as a slider's value is changed causing the containing <div> to change width. This shows that you can respond to changes in an element's size, even if they have nothing to do with the viewport. We also provide a checkbox to turn the observer off and on. If it is turned
![ResizeObserver - Web APIs | MDN](https://cdn-ak-scissors.b.st-hatena.com/image/square/aa767575b4232d312d2c5de428f0bf0955805e26/height=288;version=1;width=512/https%3A%2F%2Fdeveloper.mozilla.org%2Fmdn-social-share.cd6c4a5a.png)