Shrink them a tiny bit so they look the same size as cross.
* etc/images/symbols/minus_16.svg:
* etc/images/symbols/plus_16.svg: Shrink a bit.
<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-<path d="M13 7H3V9H13V7Z" />
+<path d="M12.5 7H3.5V9H12.5V7Z" />
</svg>
<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-<path d="M9 3H7V7H3V9H7V13H9V9H13V7H9V3Z" />
+<path d="M9 3.5H7V7H3.5V9H7V12.5H9V9H12.5V7H9V3.5Z" />
</svg>