How to get the circumscribed area of all DOM elements?

I have a lot of elements on the page. I need to draw a circumscribed rectangle that contains all DOM elements.

For that I iterate DOM elements and get rectangle:

Array.from(firstChild.children).forEach((child: Element) => {
      const rect = child.getBoundingClientRect();
});

Which props I need from rect to do that?
Logically I need to get minimal x,y of left-top corner and max bottom-right corner. But how?