How to make a shape like on image in pure css?

I need to do a shape in pure CSS like on this image. Is it impossible? Thank you! This is my code HTML:

   <div id="sm">

        <div class="group">
            <div>
                <div class="reel"></div>
            </div>
            <div>
                <div class="reel"></div>
            </div>
            <div>
                <div class="reel"></div>
            </div>



        </div>

    </div>

enter image description here