Edit in JSFiddle

div.box {
    width: 300px;
    padding: 10px;
    border: 5px solid #e9573f;
    margin-bottom: 10px;
    margin-top: 10px;
}

<div class="box">
without box-sizing
</div>

<div class="box" style="-webkit-box-sizing: content-box; -moz-box-sizing: content-box; box-sizing: content-box;">
box-sizing: content-box
</div>

<div class="box" style="-webkit-box-sizing: padding-box; -moz-box-sizing: padding-box; box-sizing: padding-box; ">
box-sizing: padding-box
</div>

<div class="box" style="-webkit-box-sizing: border-box; -moz-box-sizing: border-box; box-sizing: border-box;">
box-sizing: border-box
</div>