Looking really good.
https://validator.w3.org/nu/?doc=htt...artdemo.com%2F
https://jigsaw.w3.org/css-validator/...artdemo.com%2F
Unless you are changing the .cart-content font size when going mobile, you may want to jump it up to 16 px. Otherwise, it may be hard to read on mobile.
Other testers are complaining that you have set a min-height but not a min-width on stylesheet.css line 627. Also, the items are covered by stylesheet_zcustom.css on line 1256.
I understand that most folks know what the "hamburger" is for, but you need to have the same cursor change on hover as you do for the other icons in the header. I haven't really looked at mobile or tablet, but remember that there's no mouse involved, which means you have to use some other method to identify "tappable links".
Whether you go with one aria landmark or a landmark for each section of the opening window, it needs at least one.
It's not an error, but you might want to consider adding a closing icon at the bottom of the opening window to avoid having to return to the beginning to close the window.
jQuery CDN is really throwing a monkey wrench into page load. It's not really relevant with today's browsers but if you must, consider adding defer so pages can load much faster. With today's speed, making the customer wait for 3 seconds on a mobile phone is liable to lose them.
https://www.zencartdemo.com/index.ph...products_id=21 - Lighthouse shows 3.7s for LCP on a mobile. with jQuery CDN responsible for 1.12 s of that time.
https://www.zencartdemo.com/index.ph...e=checkout_one -- Problems on this page deal with proper labeling of table cells and form fields. Probably with your loaded version of OPC. The actual checkout page has the same table and form problem along with an added color contrast problem for Shipping Address, Same as Billing? (Try #7b11df) and Redemption Code (Try #006120).
Mentioned before -
https://www.zencartdemo.com/index.ph...roducts_id=154. You might want to find an image of some rope.
