Onebox loading spinner gif should be transparent

[jesus2099]

When using The Dark Theme, the animated gif spinner that shows up in post preview for Onebox has a white background.
So it does not look good against the dark grey background of The Dark Theme.

[codinghorror (Jeff Atwood)]

Aha, is this something we should tweak @awesomerobot?

[awesomerobot (Kris)]

I replaced the gif with our CSS loading spinner, so now this should change colors with themes

[codinghorror (Jeff Atwood)]

Awesome! Much better thanks

[jesus2099]

Oh yes, thanks so much, it now looks really great on dark theme as well!