#d1, #d2, #d3, #d4, #d5, #d6 {
  border: 1px solid blue;;
}

.blue {
  color:blue;
}

#d3, #d4 {
  display: inline;
}

#d5, #d6 {
  display: inline-block;
  height: 3em;
  width: 45%;
}

.col1, .col2 {
  display: inline-block;
  border: 0px;
  height: 3em;
  width: 50%; 
  color: red;
}

.col1 {
  background-color: yellow;
}

.col2 {
  background-color: pink;
}

.d01, .d02, .d03, .d04, .d001, .d002, .d003, .d004 {
  height: 5em; 
  width: 5em;
}

.d01, .d001 {
  background-color: red;
}

.d02, .d002 {
  background-color: blue;
}

.d03, .d003 {
  background-color: yellow;
}

.d04, .d004 {
  background-color: green;
}

.d001, .d002, .d003, .d004 {
  display: inline-block;
}

.left {
  float:left;
}

.no-float {
  clear: both;
}

/* clearfix */
/* instead of <div style="clear: both;"></div>*/
/*
.d02::after {
  content: "";
  clear: both;
  display: block;
}

*/

#div1 {
  border: 3px solid green;
  text-align: center;
}

#div2 {
  position: relative;
  border: 3px solid green;
  text-align: center;
  left: 50px;
  text-align: center;
}

#div3 {
  position: fixed;
  border: 3px solid green;
  bottom: 0;
  right: 0;
  width: 300px;  
  background-color: red;
  text-align: center;
}

div.relative {
  position: relative;
  border: 3px solid green;
  height: 300px;
  width: 300px;
  margin: 0 auto; /* center */
}

div.absolute {
  position: absolute;
  border: 3px solid green;
  top: 50px;
  right: 50px;
  width: 100px;  
  height: 100px;
  text-align: center;
}