We've covered Aspect Ratio Boxes before. It involves trickery with padding such that an element's width and height are in proportion to your liking. It's not an ultra-common need, since fixing an element's height is asking for trouble, but it comes up.
One way to lower the risk is The Psuedo Element Tactic, in which a pseudo element pushes its parent element to the aspect ratio, but if the content inside pushes it taller, it will get taller, aspect ratio be damned.
You can use that technique in CSS grid with grid items! Although there are a couple of different ways to apply it that are worth thinking about.