SOURCE

<div class="box box1">
    <div class="inner">1</div>
</div>

<div class="box box2">
    <div class="inner">2</div>
</div>

<div class="box box3">
    <div class="inner">3</div>
</div>

<div class="box box4">
    <div class="inner">4</div>
</div>

<div class="box box5">
    <div class="inner">5</div>
</div>

.box{
    height: 150px;
    width: 50%;
    float: left;
    margin-top:15px;
    background-color: #ddd;
    font-size: 34px;
    color: #ddd;
    text-align: center;
}
.box:nth-child(odd){
    background-color: #ccc;
}
.box .inner{
    height: 100px;
    width: 100px;
    background-color: #f00;
}

/* box1 */
.box1{
    position: relative;
}
.box1 .inner{
    position: absolute;
    left: 50%;
    top: 50%;
    margin-left: -50px;
    margin-top: -50px;
}

/* box2 */
.box2{
    position: relative;
}
.box2 .inner{
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%)
}

/* box3 */
.box3{
    position: relative;
}
.box3 .inner{
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto;
}

/* box4 */
.box4{
    display: flex;
    justify-content: center;
    align-items: center;
}

/* box5 */
.box5{
    display: table;
}
.box5 .inner{
    display: table-cell;
    vertical-align: middle;
}