Diseño de orden de clase en CSS3

<style>
  main {
    width: 100%;
    padding: 39px 29px;
    font-size: 12px;
  }
  section {
    width: 100%;
    box-shadow: 0 0 0 1px #eeeeee;
    display: flex;
    overflow: hidden;
  }
  section > span {
    width: 20%;
    padding: 12px;
    align-self: center;
  }
  .left {
    width: 45%;
    display: flex;
    flex-direction: column;
    padding-bottom: 0;
  }
  .center {
    width: 35%;
    padding-top: 999px;       /* h */
    padding-bottom: 999px;    /* a */
    margin-top: -999px;       /* c */
    margin-bottom: -999px;    /* k */
    border: 1px solid #eee;
  }
  .left .item {
    text-align: center;
    line-height: 85px;
    background: rgba(180,160,120,.1);
    position: relative;
    margin-bottom: 12px;
  }
</style>

  <main class="main">
    <section>
      <span class="left">
        <div
          v-for="ele in elements"
          @click="handleClick"
          class="item">
          {{symbol}}
        </div>
      </span>
      <span class="center">vertical centering<br>vertical centering</span>
      <span class="right">vertical centering</span>
    </section>
  </main>

<script>
  export default {
    data () {
      return {
        elements: Array(2).fill(1),
        symbol: '➕'
      }
    },
    methods: {
      handleClick () {
        this.elements.length == 2 ? (_ => {
          this.elements.push(1);
          this.symbol = '➖';
        })() : (_ => {
          this.elements.pop();
          this.symbol = '➕';
        })()
      }
    }
  }
</script>