Explain the concept of class and ids in CSS code example

Example 1: css class and id

Select an element with the ID "id" and the class "class":
#id.class {
}
example:

  
      Foobar
  
  
      Foobar
  

=> Will select the first  element

Select all elements with the class "class",
which are decendents of a element with an ID of "id":
#id .class {
}
example:

	Foobar

=> Will select the  element

css
.class
#id