since you are invoking an SVG image; You must also define the SVG on your page. It is also necessary to determine the height and width , as well as in your SVG, otherwise, by default, take 1em width and height, if not specified.
<svg height="16px" width="16px" viewBox="0 0 16 16" version='1.1' xmlns='http://www.w3.org/2000/svg'> </svg>
It would be best to invoke the image using background:url so that height and width can be displayed, so the SVG image can be displayed correctly.
.services li:before { content:''; display:inline-block; height:1em; width:1em; background-image:url('images/check.svg'); background-size:contain; background-repeat:no-repeat; padding-left: 2em; }
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