JSFiddle - React, Tailwind, and code Playground
HTML
<span class="expiration">
<input type="text" name="month" placeholder="MM" maxlength="2" size="2" required="true" />
<span>/</span>
<input type="text" name="year" placeholder="YY" maxlength="2" size="2" required="true" />
</span>
CSS
.expiration {
border: 1px solid #bbb;
}
.expiration input {
border: 0;
text-align: center;
outline: 0; /* remove if you want input highlight */
}