Space/ no space between css selectors and classes of elements

Question

What's the difference between the selection of a css selector (for example: p) and a class of an element (.cat)?

 p.cat{
}

vs

p .cat{
}

Thanks!!

Answer 1

1. p.cat selects paragraph elements with the cat class.
2. p .cat selects all elements with the cat class that are descendants of paragraph elements.