html how to center div on page code example

Example 1: center div horizontally and vertically

.parent {
  position: relative;
}
.child {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

Example 2: how to center a div element

/*ADD MARGIN auto to left and right*/
.box1{
    width:80%;
    margin:0 auto;
}

Example 3: html position div inside div

.textblock-container {
width: 500px;
height: 500px;
border: 1px solid red;
position: relative;
}

div.textblock {
width: 100px;
height: 100px;
line-height: 100px;
border: 1px solid black;
position: absolute;
text-align: center;             
background: rgb(0, 150, 0);
background: rgba(0, 150, 0, .5);
}