[css layout][06] three percentage columns

1.#wrapper宽度100%全部float向左

#wrapper {
  width: 100%;
  float: left;
}
#content {
  margin-left: 50%;
}
#navigation {
  float: left;
  width: 25%;
  margin-left: -75%;
}
#extra {
  float: left;
  width: 25%;
  margin-left: -100%;
}
#footer {
  clear: both; 
}

2.#wrapper宽度100%全部float向右

#wrapper {
  width: 100%;
  float: right;
}
#content {
  margin-left: 50%;
}
#navigation {
  float: right;
  width: 25%;
  margin-right: -50%;
}
#extra {
  float: right;
  width: 25%;
  margin-right: -25%;
}
#footer {
  clear: both; 
}

3.#wrapper宽度50%全部float向右

#wrapper {
  width: 50%;
  float: right;
}
#navigation {
  float: right;
  width: 25%;
}
#extra {
  float: right;
  width: 25%;
}
#footer {
  clear: both; 
}

4.#wrapper宽度50%全部float向左

#wrapper {
  width: 50%;
  float: left;
  margin-right: -50%;
  position: relative;
  left: 50%;
}
#navigation {
  float: left;
  width: 25%;
  margin-right: -25%;
  position: relative;
  left: 25%;
}
#extra {
  float: left;
  width: 25%;
}
#footer {
  clear: both; 
}