<div class="content">
  <span class="frac">
    <span class="frac-num">A</span>
    <span class="frac-div">/</span>
    <span class="frac-den">B</span>
  </span>
</div>
.content { font-size: 30px; padding: 30px; text-align: center; }

.frac {
    align-items: stretch;
    display: inline-flex;
    flex-direction: column;
    font-size: 0.75em;
    line-height: 1;
    margin: 0 0.2em;
    text-align: center;
    vertical-align: middle;
}
 
.frac-div {
    border-bottom: 1px solid #000;
    color: transparent;
    height: 1px;
    margin: -0.1em 0 0.3em;
}

External CSS

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External JavaScript

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