This issue was originally raised in typst/svg2pdf#96. Apparently, resvg does not properly handle text-shadow.
MRE:
<svg width="300" height="100" xmlns="http://www.w3.org/2000/svg">
<style>
.shadowed {
font-size: 40px;
fill: black;
text-shadow: black 5px 5px 5px;
}
</style>
<text x="50" y="50" class="shadowed">Shadow Text</text>
</svg>