JSFiddle - React, Tailwind, and code Playground

HTML

<script language='javascript' type='text/javascript'>

    function changeCssClass(objInputID, currentVal, correctVal)
    {               

                if(correctVal == currentVal)
        {
                    document.getElementById(objInputID).className = 'show';
        }
        else
        {
            document.getElementById(objInputID).className = 'hide';
        }
    }

    </script>
<p>Select a Grade:</p>
<select name="grade" id="grade" onchange="changeCssClass('otherGrade', this.value, 'otherGrade')">
<option value="No Specified Grade">Please Select</option>
<option value="201">201</option>
<option value="Secondary">Secondary</option>
<option value="otherGrade">Other</option>
</select>

<p>If "Other":</p>

<input type="text" name="otherGrade" id="otherGrade" class="hide" />

CSS

.hide{display:none;}
.show{display:normal;}