Validation without JavaScript in HTML & CSS
HTML & CSS interview exercise on Forms, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
A profile form the browser validates on its own: a required username of 3 to 20 characters made of lowercase letters, digits and dashes only (a pattern); a required website URL; and an optional phone field that brings up the phone keypad on a phone. Label all three.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.