The vw unit is useful when we want to
define width of elements based on the screen
width.
Take a look at the following example:
vw is used here for the font-size
because we want the text size to change
proportionally with the change in the width
of the viewport.
Open this code and
drag to change the width. You'll see that
the size of the text increases properly
with the change in the width of the viewport.