Your problem is that your viewBox
is not set to appropriate values.
It is set to have 800 width and 800 height. But your content is nowhere near that big.
If we colour the background of the SVG we can see that.
svg {
width: 400px;
background-color: linen;
}
<svg version="1.1" style="display: block;" viewBox="0 0 800 800">
<defs>
<!-- The text path: see links above regarding coordinate system -->
<path d="M0, 200a200, 200 0 1, 0 400, 0a200, 200 0 1, 0 -400, 0" id="txt-path"></path>
</defs>
<text fill="black" font-size="45.5" font-family="moholregular">
<!-- This is the magic -->
<textPath startOffset="0" xlink_href="#txt-path">Try our all new baby name generator</textPath>
</text>
</svg>
The viewBox
should be set to values that are tighter around the graphic.
For example: viewBox="-10 151 420 260"
.
svg {
width: 400px;
background-color: linen;
}
<svg version="1.1" style="display: block;" viewBox="-10 151 420 260">
<defs>
<!-- The text path: see links above regarding coordinate system -->
<path d="M0, 200a200, 200 0 1, 0 400, 0a200, 200 0 1, 0 -400, 0" id="txt-path"></path>
</defs>
<text fill="black" font-size="45.5" font-family="moholregular">
<!-- This is the magic -->
<textPath startOffset="0" xlink_href="#txt-path">Try our all new baby name generator</textPath>
</text>
</svg>