Create a rule for h3 tags and inside the braces set the color: green;.

<html> <head> <style> h3 { color: green; } </style> </head> <body> <h1>Contents</h1> <h3>The etymology of the word green</h3> <h3>Where do green pigments come from</h3> <h3>The wavelength of the color green</h3> </body> </html>]]>

Make sure to pick h3 followed by { and then color: green;, }.