How to make a blurry background CORRECTLY?

Question

css

I want to implement the same background blur on my site, but I don't know how to do it right.
I've been googling for 20 minutes now, I've looked at many sources, but I haven't seen any high-quality code anywhere.

Good people, tell me how to implement this correctly?
Thanks to.

Answer 1

.selector {
    filter: blur(5px);
}