JSFiddle - React, Tailwind, and code Playground

HTML

<div class="navigation">
            <a class="link" href="javascript:slideonlyone('newboxes1');" >slide this one only</a>

            <a class="link" href="javascript:slideonlyone('newboxes2');" >slide this one only</a>
              
            <a class="link" href="javascript:slideonlyone('newboxes3');" >slide this one only</a>
    
    

</div>

CSS

.navigation a {
    text-decoration: none;
}
.navigation a:hover {
    text-decoration: none;
}
.navigation .underline {
    text-decoration: underline;        
}
.newboxes {
    border: 1px solid black; 
    background-color: #CCCCCC; 
    display: none;
    padding: 5px;
}
.headerdiv {
    border: 1px solid blue; 
    background-color: #99CCFF; 
    padding: 5px;
}
.close{
	float: right;
    cursor: pointer;
}

JavaScript

function slideonlyone(thechosenone) {
     $('.newboxes').each(function(index) {
          if ($(this).data("id") == thechosenone) {
               $(this).show(200);
          }
          else {
               $(this).slideUp(600);
          }
     });
}

$(document).ready(function() {
    $('.navigation').on('click', 'a.link', function() {
        $('a.link').removeClass('underline');
        $(this).addClass('underline');
    });      
    $('.navigation').on('click', '.close', function() {
        $('.newboxes').slideUp(600);
    });
});