Specifically, I was able to target td-login-modal-wrap, and .mfp-container, and elements within #td-login-div like td-login-form-div, .td-login-button, etc to style the popup generated on desktop when that Header login element is clicked.

What I couldn’t find through any means I used, was what containers and elements were called when generating the mobile version.

Hello. I’m sorry, your response doesn’t make a lot of sense to me. I am using a hamburger menu for the categories list, yes. For the log in menu, I am using the “Header login” element. I know the pop up is mobile – I was able to style the desktop version, but what I can’t discern is how and where to style the mobile version of the popup.