JSFiddle - React, Tailwind, and code Playground

HTML

<div class="pro3a">
    
    <button type="submit" id="related-btn" title="Vis relaterte produkter" value="">{t _recommended}</button> 
</div>

<div id="show-hide">
    <div id="relatedProducts">
        
        {foreach from=$related item=group}
        
        {if $group.0.ProductRelationshipGroup.name_lang}
        <h3>{$group.0.ProductRelationshipGroup.name_lang}</h3>
        {/if}
        
        {include file="category/productList.tpl" products=$group}
        
        {/foreach}
        
    </div>
</div>
</div>

CSS

.pro3a {
    padding:0px;
    margin-top:10px;
    margin-left:18px;
    color:#3B88CB;
    font-size: 16px; 
    font-weight: thinner;
    white-space: nowrap;
    display: block;
}

#show-hide
{
    display:none;
    margin: 0;
    padding: 0;
    clear:both;
}

#show-hide .highlighted
{
    display:block;
    margin: 0;
    padding: 0;
    clear:both;
}

#related-btn
{
    margin: 0;
    padding: 0;
    background-image: url(../../upload/down_chev.png);
    background-repeat:no-repeat;
    background-position: right;
    background-color:#ffffff;
    padding-right: 20px;
    border:none;
    overflow:hidden;
    outline:none;
    white-space: nowrap;
    height:30px;
    cursor:pointer;
    display:block;
    color:#3B88CB;
    font-size: 16px; 
}

#related-btn:hover 
{
    margin: 0;
    padding: 0;
    background-image: url(../../upload/down_chev.png);
    background-repeat:no-repeat;
    background-position: right;
    background-color:#ffffff;
    padding-right: 20px;
    border:none;
    overflow:hidden;
    outline:none;
    white-space: nowrap;
    height:30px;
    cursor:pointer;
    display:block;
    color:#333;
    font-size: 16px;  
}

.chev-up
{
    /*background-image: url(../../upload/down_chev.png) !important;*/
    color: #00f;
}

JavaScript

$(function() {
    $("#related-btn").click(function() {
        $("#show-hide").toggle("slow");
    });
});

$(function() {
    $("#related-btn").click(function() {
        $("this").toggleClass("chev-up");
    });
});