When editing elements of your page such as font size or margins, you might notice that some measurement values are not using pixel which is an absolute unit, but instead uses em/vh/vw, which are relative units.
The difference between absolute units (px) and relative units (em/vh/vw) is that pixels remain the same regardless of the screen size.
For example, 1 pixel on a small mobile screen, and 1 pixel on a big 4K screen will occupy the exact same amount of space. On the other hand, when using em/vh/vw units, the elements are been adjusted to the screen size automatically. This way, the size of your text, the distance between elements, etc... will be relative depending on the screen size meaning that your website will adapt mostly to any device out there! This improves the responsiveness of the platform a lot.
Note: it's possible to use the arrows on the keyboard to select a precise number if you find it difficult with the slider.