Answers for "how to align div horizontally"

css center

/* this will center all children within the parent element. */
.parent {
  display: flex;
  justify-content: center; /* horizontal */
  align-items: center; /* vertical */
}

center div horizontally

/* margin auto does the magic, make sure to provide width less than 100% */
.center {
	margin: auto;
    width: 400px;
}

.center {
	margin: auto;
    width: 50%;
}

vertical align css

.container{
  display: table;
}

.div-inside-container{
  display: table-cell;
  vertical-align: middle;
}