Base-apparel-with-CSS_grid & jqeury

What are the new things I learn in this project? CSS grid, Validation, settimeout, a little bit more about positioning.

I am still confused about which is a suitable unit(%, rem, px) to use in height-width, and padding-margin. I use jquery to validate the form but am not sure how to select the input type email in jquery so I used a #selector in jquery. if any of you know about please let me know. Also, how to make error messages stay there when input is not matched with regex and when a user enters again email address that does not match with regex error shakes again. I make this with set timeout function. it'll be great and helpful for me if you give your valuable feedback about my concerns.