SVG is not displayed correctly when adding it to pdfmake pdf

[EdoardoCroci]

I have a react project with pdfmake added by yarn, a component draws a chart (svg) using d3, I use an id to get the svg.
This is how I get the svg and add it to an empty document:

const svgElement = document.getElementById('svgConcrete');
const svgString = svgElement.outerHTML;

const docDefinition = {
  content: [           
    {
      columns: [
        { width: '*', text: '' },
        {
          svg: svgString,
          width: 175,
          height: 175
        },
        { width: '*', text: '' },
      ]
    }
  ],
}

The image that should be displayed is this:

The image that I get is:

Why does this happen? How can I fix it?