When length is specified using vw,
it is calculated based on the window width,
also known as viewport width.
Viewport is the visible part of a screen.
In the example given below, the viewport is
the rectangular window given below the
code editor and, the div covers 50%
of the width of 100vw and has the same height.
1vw is 1% of the window width.
So, 100vw is equivalent to the window width.