Why do some sites look COMPLETELY different in different browsers? missed something in the field of layout and design?

Question

css

Some sites, for example "socket", have a completely different interface depending on which browser I use. And not only the type of browser matters. I opened one site in latest chrome in main OS and in VM in same chrome. And got two completely different sites.
The differences are mainly in the elements of interaction with the page. Ie selectors checkboxes and all that.
I have only one explanation: now for each browser they write separate templates and a separate design. This is true?

Answer 1

Usually applications from the category of "bloody enterprise" suffer from such things.
You must always keep it working. Here they make crutches.