#div1 {
    width: 100%;
    min-width: 400px;
    outline: blue;
}
#div2 {
    width: 300px;
    margin: 0 auto;
    outline: 1px solid #ccc;
    color: white;
}

<div id="div1" class="cw">
    <div id="div2">
        test
    </div>
</div>

.cw {
    background:blue  linear-gradient(
    to right, red calc(50% - 150px + 60px ) ,
    transparent calc(50% - 150px + 60px )
    );
}