Question

I want a CSS layout where there is a side-bar on the left-hand side which is 100px. The entire web page must be 400 px wide. What are the pros, cons and general differences between the following different methods?

Method 1

#container {
  width: 400px;
}

#left {
  float: left;
  width: 100px;
}

#main {
  float: left;
  width: 300px;
}

Method 2

#container {
  width: 400px;
}

#left {
  float: left;
  width: 100px;
}

#main {
  display: block;
  margin-left: 100px;
}

Answer 1

You should go with method number 1,

and assuming #main is a div, it already has a property of display:block; by default.