一、Is it inline or inline-* elements (like text or links)? 是否行内元素
(1).Is it a single line? 单行文本垂直居中：
1.padding
.link {
padding-top: 30px;
padding-bottom: 30px;
}
2.line-height
.center-text-trick {
height: 100px;
line-height: 100px;
white-space: nowrap;
}
(2).Is it multiple lines? 多行垂直居中：

1. display: table-cell;
   <div class="center-table">
   <p>I'm vertically centered multiple lines of text in a CSS-created table layout.</p>
   </div>
   <style>
   .center-table {
   display: table;
   height: 250px;
   background: white;
   width: 240px;
   margin: 20px;
   }
   .center-table p {
   display: table-cell;
   margin: 0;
   background: black;
   color: white;
   padding: 20px;
   border: 10px solid white;
   vertical-align: middle;
   }
   </style>
   代码：https://codepen.io/chriscoyier/pen/ekoFx
   2.flex
   不支持ie10以下，android 4.4以下，Safari Mobile 7.1以下
   .flex-center-vertically {
   display: flex;
   justify-content: center;
   flex-direction: column;
   height: 400px;
   }
   3.vertical-align: middle
   ::before support不支持ie9以下，注意 :before Safari Mobile不支持。
   .ghost-center {
   position: relative;
   }
   .ghost-center::before {
   content: " ";
   display: inline-block;
   height: 100%;
   width: 1%;
   vertical-align: middle;
   }
   .ghost-center p {
   display: inline-block;
   vertical-align: middle;
   }
   二、Is it a block-level element? 是否块元素
   (1).Do you know the height of the element?
   .parent {
   position: relative;
   }
   .child {
   position: absolute;
   top: 50%;
   height: 100px;
   margin-top: -50px; /* account for padding and border if not using box-sizing: border-box; */
   }
   (2).Is the element of unknown height?
   .parent {
   position: relative;
   }
   .child {
   position: absolute;
   top: 50%;
   transform: translateY(-50%);
   }
   (3).Can you use flexbox?
   .parent {
   display: flex;
   flex-direction: column;
   justify-content: center;
   }
   参考：https://css-tricks.com/centering-css-complete-guide/

附scss mixin：
.element {
position: relative;
top: 50%;
transform: translateY(-50%);
}

/* scss Mixin */
@mixin vertical-align($position: relative) {
position: $position;
top: 50%;
-webkit-transform: translateY(-50%);
-ms-transform: translateY(-50%);
transform: translateY(-50%);
}

.element p {
@include vertical-align();
}

from:http://zerosixthree.se/vertical-align-anything-with-just-3-lines-of-css/