css flex center

display: flex;
align-items: center;
justify-content: center;/* Answer to: "css flex vertical align" */

.box {
  display: flex;
  align-items: center; /* Vertical */
  justify-content: center; /* Horizontal */
}

.box div {
  width: 100px;
  height: 100px;
}

/*
  For more information go to:
  https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flexible_Box_Layout/Aligning_Items_in_a_Flex_Container
*/.primary-nav {
    display:-webkit-flex;
    display:flex;
    list-style-type:none;
    padding:0;
    justify-content:flex-end;
}

.left {
    margin-right:auto;
}