<iframe
src="//www.epa.gov/sites/production/files/widgets/earthdaycountdown.html"
id="earthdaycountdown"
width="150"
height="100"
scrolling="no"
frameborder="0"
marginwidth="0"
marginheight="0"
vspace="0"
hspace="0"
allowtransparency="true">
</iframe>

Shows how many days remain until the next Earth Day (April 22).