Scale div into div like background image

I'm working on a web app and now facing a rather tricky task. I have an image that I have to add overlay for.

Let's say I have an image of a car. I need to add values, like outside and inside temperature, on top of the car image.

It would be easy to add fixed pixel offsets for those temperature labels, but the image need to be scalable to every screen height and width-wise. I can't think of easy way to scale div into div exactly as "background-size:contain;" does for images.

Could someone point me to right tracks before I write complex javascript scaling logic?