<p>
<button class="btn btn-danger collapsed" data-target="#demo" data-toggle="collapse" type="button">CLICK HERE!</button>
</p>
<div style="height: 0px;" id="demo" class="collapse">
<img src="https://tesol.lcms.vn/pluginfile.php/53112/mod_page/content/2/best%204.png" alt="" ></img>
</div>