title: css header layout width 3 divs
body: <p>I am trying to create a header with 3 divs: one is aligned left, one is aligned right and the other is in the center. <img src="https://i.stack.imgur.com/RIzxd.png" alt="enter image description here"></p>
  
  <p>the page is for example 1200px
  the black,red and yellow rectangles are 960px and centered in the page.
  elements in the black rectangle are added to the left,
  elements in the yellwo rectangle are added to the right,
  and the elements in the red tectangle are centered.</p>
  
  <p>This is a good general case study for header of a site</p>