Tryit Editor v1.8

Source Code:
<!DOCTYPE html> <html> <head> <style> p:nth-child(2) { background:#ff0000; } </style> </head> <body> <h1>This is a heading</h1> <p>The first paragraph.</p> <p>The second paragraph.</p> <p>The third paragraph.</p> <p>The fourth paragraph.</p> <p><b>Note:</b> Internet Explorer 8 and earlier versions do not support the :nth-child() selector.</p> </body> </html>
Result:
W3Schools.com - Try it yourself