Is it possible to create this shape (two partial circles joined together) with CSS?

SVG

This is also possible using SVG.

The SVG version is very short as it mainly only requires an Arc command to control its shape, size and position.

<svg width="50%" viewbox="0 0 100 50">
  <path d="M50,35 
           a20,20 0 1,0 0,-20 
           a20,20 0 1,0 0,20z" 
        fill="white" 
        stroke="black">
  </path>
</svg>

SVG stands for Scalable Vector Graphic. The web browser views it as an image but you can add text and normal HTML elements within an SVG.

It is well supported across all browsers as viewable here: CanIUse

• SVG | MDN