.wrapBox5{
    width: 300px;
    height: 300px;
    border:1px solid red;
    position: relative;
}
.wrapItem5{
    width: 100px;
    height: 50px;
    position: absolute;
    background:yellow;
    top: 50%;
    left:50%;
    margin-top: -25px;
    margin-left: -50px;
}

.wrapBox{
    width: 300px;
    height: 300px;
    background: yellow;
    position: relative;
}
.wrapItem{
    width: 100px;
    height: 50px;
    background:green;
    display: inline-block;
    position: absolute;
    top: 0px;
    bottom:0px;
    left: 0px;
    right: 0px;
    margin:auto;
}

.wrapBox6{
    width: 300px;
    height: 300px;
    border:1px solid green;
    position: relative;
}
.wrapItem6{
    width: 100px;
    height: 50px;
    position: absolute;
    background:yellow;
    top: calc(50% - 25px);
    left:calc(50% - 50px);
}

.wrapBox{
    width: 300px;
    height: 300px;
    background:#ddd;
    position: relative;
}
.wrapItem{
    width: 100px;
    height: 50px;
    background:green;
    position: absolute;
    top: 50%;
    left:50%;
    transform: translate(-50% , -50%);
}

.wrapBox2{
    width: 300px;
    height: 300px;
    background: blue;
    display: flex;
    justify-content: center;
    align-items: center;
}
/*注意：即使不设置子元素为行块元素也不会独占一层*/
.wrapItem2{
    width: 100px;
    height: 50px;
    background:green;
}

.wrapBox3{
    width: 300px;
    height: 300px;
    background: yellow;
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}
.wrapItem3{
    width: 100px;
    height: 50px;
    background:green;
    display: inline-block;
}

.tableBox{
    border:2px solid yellow;
    width: 300px;
    height: 300px;
}
.tableBox table{
    width:100%;
    height:100%;
}
.centerWrap{
    text-align: center;
    vertical-align: middle;
}
.centerItem{
    display: inline-block;
    background:pink;
}