Loading toast spinner

[emilybrick]

Earlier options:

Thoughts:

Yellow feels like the right color here, but curious if others think it's a bad idea to keep the same style as the warning toast. I can see it working for pending and/or warning states.

• landed on gray here as to not confuse this with a warning!

Leaning on the third option after chatting with @ashygee but open to discuss!

• decided to stick with the circle style loader

Updated iteration:

[vercel]

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[emilybrick]

The latest iteration is pushed up!
Based on feedback in our design systems design review last night, I'm opting for a gray background on the --loading modifier class:

The loading circle is $gray-400, the rotating slice in the circle is white, and the background is $gray-600

[emilybrick]

@shawnbot I think this is ready for review 🙏

[shawnbot]

This looks great. Can't wait to see it in use! Let's merge this to #854.