numix-gtk-theme/gtk-3.0/assets/checkbox-mixed-insensitive-dark.svg

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="translate(0 -1036.3622)">
<path style="fill:#2a2a2a" d="m 1.7429523,1036.9203 12.7034987,0 c 0.586479,0 1.058625,0.468 1.058625,1.0495 l 0,12.5953 c 0,0.5815 -0.472146,1.0496 -1.058625,1.0496 l -12.7034987,0 c -0.5864782,0 -1.05862497,-0.4681 -1.05862497,-1.0496 l 0,-12.5953 c 0,-0.5815 0.47214677,-1.0495 1.05862497,-1.0495 z"/>
</g>
<g style="fill:#1f1f1f" transform="translate(0 -1036.3622)">
<path d="M 2 0 C 0.892 0 3.2526065e-18 0.892 0 2 L 0 14 C 0 15.108 0.892 16 2 16 L 14 16 C 15.108 16 16 15.108 16 14 L 16 2 C 16 0.892 15.108 3.2526065e-18 14 0 L 2 0 z M 2 1 L 14 1 C 14.554 1 15 1.446 15 2 L 15 14 C 15 14.554 14.554 15 14 15 L 2 15 C 1.446 15 1 14.554 1 14 L 1 2 C 1 1.446 1.446 1 2 1 z " transform="translate(0 1036.3622)"/>
<rect width="8" x="4" y="1043.362" height="2"/>
</g>
</svg>