An example implementing the vertical alignment

vertical-align.css

/* absolution position + transform approach */
.parent {
  height: 100vh;
  position: relative;
  
  .children {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
}

/* display table approach, working for min height on parent */
.parent {
  display: table;
  min-height: 100vh;
  
  .children {
    display: table-cell;
    vertical-align: middle;
  }
}