JSFiddle - React, Tailwind, and code Playground

HTML

<select size="4" name="ItemContainerBox" id="ItemContainerBox" class="FTP_Content">      
   <option value="test1" class="FTP_Item noSelect">test1</option>
   <option value="test2" class="FTP_Item noSelect">test2</option>
   <option value="test3" class="FTP_Item noSelect">test3</option>
   <option value="test4" class="FTP_Item noSelect">test4</option>
</select>

CSS

/* make it red instead (with with same width and style) */
 select option:checked {
        background: linear-gradient(#F8F8FF, #F8F8FF);
        background-color: #F8F8FF !important;
        
        color: black;
        -webkit-text-fill-color: black;
    }