Sublime Text
<!DOCTYPE html> <html> <head> <style type="text/css"> input[type="text"]:optional{ background-color: yellow; } </style> </head> <body> <input type="text" required> <br><br> <input type="text"> </body> </html>
<!DOCTYPE html> <html> <head> <style type="text/css"> input[type="text"]:optional{ background-color: yellow; } </style> </head> <body> <input type="text" required> <br><br> <input type="text"> </body> </html>