Answers for "how to set element html contents vertically"

css align items vertical center

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

vertical align into div

#parent {position: relative;}

#child {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    width: 50%;
    height: 30%;
    margin: auto;
}