CSS Margin: 0 is not setting to 0

Question

I\'m a new comer to web designing. I created my web page layout using CSS and HTML as below. The problem is even though i set the margin to 0, the upper margin is not settin

Answer 1

add this code to the starting of the main CSS.

*,html,body{
  margin:0 !important;
  padding:0 !important;
  box-sizing: border-box !important;;
}