垂直居中

.arpb {width: 100%;height: 100%;position: fixed;top: 0;left: 0;background-color: rgba(248,248,248,0.9);z-index: 9999;}

.arpb .arc {position: absolute;left: 50%;width: 100%;height: 100%;max-width: 20rem;min-width: 10rem;display: table;}

.arpb .arc .arci {display: table-cell;vertical-align: middle;}

<div id="note_main" class="arc_main"><div class="arpb"><div class="arc"><div class="arci"><div class="about_cont">垂直居中</div></div></div></div></div>