How can I display the text from the selected <option>'s <optgroup> on the dropdown when it is not in focus?

Currently it looks like this when not in focus:

When it is in focus it looks like this:

If possible I'd like it to show "Hepatitis B - Core antibody blood test" when it is not in focus.

Is there any way to do this?

The code currently looks something like this:

<select name="bloodsVaccinesTypesBloods-${newRowId}" id="bloodsVaccinesTypesBloods-${newRowId}" class="bloodsVaccinesDropdown bloodsVaccinesTestTypes bloodsVaccinesTypesBloods">
    <optgroup label="Hepatitis B">
        <option value="12" selected="selected">Antigen blood test</option>
        <option value="13">Core antibody blood test</option>
        <option value="10">Vaccine (course of 3 vaccines & 5 year booster)</option>
    <optgroup label="Hepatitis C">
        <option value="14">Antibody blood test</option>
        <option value="15">RNA blood test</option>
    </optgroup>
</select>