[][1]
Compared to the size of the voting buttons and score, it's unusually (unlike the checkmark on other Stack Exchange sites) large.
I'd consider this to be a bug. If it's not a bug, then it's a feature request.
<sarcasm>
If the purpose was to show off the checkmark though, apologies. Then you should probably enlarge it, as suggested by bjb:
</sarcasm>
[1]: https://i.sstatic.net/TEA1s.png