how to place div centered inside div?

You can simply place horizontally aligned div inside div(without using position: absolute) by using margin:0 auto property in CSS

Code

.MainDiv{
  width: 100%; 
}

.InnerDiv{
  display: table;
  margin: 0 auto;
}

Another alternative method to horizontally centralizing div is using the below css code

CSS

.MainDiv{
  width: 100%;
  text-align: center;
}

.InnerDiv{
  display: inline-block;
}

the above code will place .InnerDiv in the middle