How to place a red background color on a form field when there is an invalid input

Hello,

Good day everyone, i am new to JQuery and i am learning how it works. i stumbled upon the validate function of JQuery.

as of now, i am creating a simple form validation script where i will ask for the username, password and email of a user. when an error is created, a text will be displayed beside the textbox. but i want to know how i can add colors to the textbox if there is an error. thank you for your help.