The official D3 logo is available is several forms in the d3-logo repository.
<!DOCTYPE html>
<meta charset="utf-8">
<img width="960" height="500" src="d3.svg">
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</clipPath>
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<stop offset="0" stop-color="#f9a03c"/>
<stop offset="1" stop-color="#f7974e"/>
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<linearGradient id="gradient-2" gradientUnits="userSpaceOnUse" x1="2" y1="-2" x2="87" y2="84">
<stop offset="0" stop-color="#f26d58"/>
<stop offset="1" stop-color="#f9a03c"/>
</linearGradient>
<linearGradient id="gradient-3" gradientUnits="userSpaceOnUse" x1="45" y1="-10" x2="108" y2="53">
<stop offset="0" stop-color="#b84e51"/>
<stop offset="1" stop-color="#f68e48"/>
</linearGradient>
<g clip-path="url(#clip)">
<path d="M-100,-102m-28,0v300h300z" fill="url(#gradient-1)"/>
<path d="M-100,-102m28,0h300v300z" fill="url(#gradient-3)"/>
<path d="M-100,-102l300,300" fill="none" stroke="url(#gradient-2)" stroke-width="40"/>
</g>
</svg>