Answers for "how to center a content in css"

center div horizontally and vertically

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

align div content center

.child {
  ...
  margin: 0 auto;
}

css align center

.center {
  margin: auto;
  width: 50%;
  border: 3px solid green;
  padding: 10px;
}