JSFiddle - React, Tailwind, and code Playground

HTML

<div style="cursor:pointer;color:bleu;" onclick="body.className='bleu';">Ambiance bleu</div>
<div style="cursor:pointer;color:vert;" onclick="body.className='vert';">Ambiance verte</div>
<div id="contact">Show me</div>

<a style="cursor:pointer;color:violet;" onclick="body.className='contactexp';">Click</a>

CSS

.bleu {
    background: blue;
}
.vert {
    background: green;
}
.violet {
    background: purple;
    ;
}
#contact {
    color: #fff;
}
#contact.contactexp {
    color: #666!important;
}