I tried a little experiment to make a popup using a details element. The goal was to see if I could make a clickable popup without using JavaScript. It should be accessible for both sighted users and users using a screen reader like NVDA.

The HTML test case is a form with an info icon (the letter I in a circular blue field) after an input element. It is straightforward semantic HTML. The details element has a summary as its first element and a div enclosing paragraphs as the details' body. The summary element is the letter I styled using CSS to put the I (for info) on a circular lightblue field. The form looks like: