how to align div in html code example

Example 1: css align center

//HTML

	Hello World


//CSS
.parent {
  display: flex;
  justify-content: center;
  align-items: center;
}

Example 2: div center

#inner {
  display: table;
  margin: 0 auto;
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%
}