What is the difference between #header{} and #header img{} in css

Question

if we call this id <div id="header">

Answer 1

#header img {} Selects all <img> elements inside id header div elements where

Answer 2

#header apply css on div and
#header img will apply css on all image inside that div

Answer 3

While we are not calling #header img it will be applied by calling <div id="header">