      <style is="custom-style" include="iron-flex iron-flex-reverse iron-flex-factors iron-flex-alignment iron-positioning">
        body {
          margin: 0;
          padding: 0;
        }
        .container {
          width: 300px;
          min-height: 50px;
          background-color: #ccc;
        }
        .container > div {
          width: 50px;
          min-height: 50px; /* so that it can grow in vertical layouts. */
        }
        /* IE11 does not calculate flex proportions correctly in a 