레이어를 정 중앙에 위치시키는 css

position: fixed;
top: 50%;
left: 50%;
-webkit-transform: translate(-50%, -50%);
-ms-transform: translate(-50%, -50%);
-moz-transform: translate(-50%, -50%);
-o-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);


데모) https://codepen.io/min9nim/pen/QVmKWR

See the Pen modal_alert by Song, MinGu (@min9nim) on CodePen.