CSS3等分div

body,p{margin: 0;}
.parent{display: flex; width:1200px; margin:0 auto;}
.child{flex:1;height: 100px;}
.child + .child{margin-left: 20px;}

    <div class="parent" style="background-color: lightgrey;">
        <div class="child" style="background-color: lightblue;">1</div>
        <div class="child" style="background-color: lightgreen;">2</div>
        <div class="child" style="background-color: lightsalmon;">3</div>
        <div class="child" style="background-color: pink;">4</div>
        <div class="child" style="background-color: pink;">5</div>
        <div class="child" style="background-color: pink;">6</div>
    </div>