Reverse engineering fuzzy mode

I recently came across Paco's website, which I adore for its simplicity, elegance, and meticulous attention to detail. One of those details is a fuzzy reading mode. Triggered by a shortcut (alt on Paco's website), certain website elements get blurred out. Try the feature on my website using 'ctrl+z'. Only the element we let our mouse pointer hover over will be visible.

My very next thought was "wow, I need this on my website". So I started reverse engineering the feature.I call it reverse engineering, some people might call it getting inspiration, yet other people will plainly call it stealing ¯ct°_o)/¯ There are two challenges to overcome: firstly, figuring out how to blur out text elements and only show ones we hover over. Secondly, activate and de-activate fuzzy mode by using a customised shortcut.

Blurring out text elements can be done using CSS. I had this suspicion already when I saw that hovering unblurred elements. A simple :hover selector would be the perfect thing to use to this end. I opened the developer tools to inspect the styling of the website and saw my suspicions confirmed:

.alt :where(p, pre, li, img, div, blockquote) {
  opacity: 0.6;
  filter: blur(2px);

.alt :where(p, pre, li, img, div, blockquote):hover {
  opacity: 1;
  filter: none;

These few lines select the elements in :where() within an HTML element of class .alt and apply the specified styling properties. So far so easy.

Triggering the reading mode with a shortcut was slightly more challenging. The goal is to add the .alt class to an element which is a parent element to all the elements we want to potentially blur out and include in the :where() selector. I chose to use the react library react-hotkeys for this purpose. Here is an excerptTo be precise, not all of this code is within the same file anymore as I separated the use cases. from my post.js template which is used to generate all writings pages on this website: Please note that my JavaScript and react skills are still very undeveloped, I've never officially learned how to use either of those.

const keyMap = 'alt'
const [fuzzy, setFuzzy] = useState(false)
const readingModes = {
    FUZZY: fuzzy
const postHotKeyHandlers = {
    FUZZY: () => setFuzzy((prev) => !prev)


<GlobalHotKeys keyMap={keyMap} handlers={postHotKeyHandlers}>

          <article className={getReadingModeClass(readingModes)}>

There are a few things to notice here. We want to keep track of whether fuzzy mode is activated or not. We use the react hook useState() for this purpose as it allows us to keep track of the value of fuzzy even when it's already passed to an element's class name in the render function later on. Furthermore, I implemented it in a way that it'll be an easy task to add additional reading modes (hence the dictionary structure and not a simple boolean variable). getReadingModeClass() is a simple helper function which returns an appropriate class string.

This was a fun way of spending an hour of my free time after work! And to repeat, full credits to Paco for this fantastic idea and the CSS.