Incorrect thumbnail border

[pRdm]

It appears that this css change caused a regression where the default Chrome button borders are now appearing:
43f3d6e#diff-4a1fd173378d19262dca5c2d053630e451aab210800b5f6f884170de07a7bc43L346

Example screenshot (using v1.4.4)

[laozhu]

I have the same problem here, I submit a PR to fix it, wish @peterpalau to approve it.