how center div in css

.container {
  display: flex;
  justify-content: center;
  align-items: center;
}

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

  .center {
  display: flex;
  justify-content: center;
  
  align-items: center;
  height: 200px;
  border: 3px solid 
  green; 
} 

.center
{

  margin: auto;

   
width: 50%;

   
border: 3px solid green;
  padding: 10px;

} 

.shadoww .prt {
    margin: 0 auto;
}