<!DOCTYPE html> <html> <head> <title>CSS level4 Selector :required and :optional</title> <link rel="author" title="LEE YUN HEE" href="mailto:zzirasi@gmail.com"> <style> input {border:3px solid green;} </style> </head> <body> <p> You should see a green input box. </p> <p> <input> </p> <p> <input> </p> </body> </html>