div {

        border: 1px solid red;

    }

    .inner {

        width: 80px;

        height: 80px;

        float: left;

        position: relative;

        margin-left:;

    }

    .inner1 {

        margin-left: 20px;

    }

    .myDiv {

        width: 100%;

        margin: 0 auto;

    }

    <div class="myDiv">

        <div class="outer">

            <div class="inner inner1">1</div>

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

        </div>

    </div>

$(function() {

    window.setTimeout(function() {

        $(".myDiv").css("width", "500px");

    }, 1000)

});