Bottom-Center Snackbar is max 50% width at mobile breakpoints

[mattd]

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

At mobile breakpoints, a <Snackbar /> positioned bottom-center should span the whole width of the window.

Current Behavior

At mobile breakpoints, a <Snackbar /> positioned bottom-center takes up at maximum the center 50% of the window. If the message is shorter than ~50% of the window, the snackbar will be smaller.

Steps to Reproduce (for bugs)

This bug is visible in the demo site under the "Positioned" section: https://material-ui-1dab0.firebaseapp.com/demos/snackbars/#positioned

1. Click "Bottom-Center".
2. Observe that the Snackbar is centered and not full width.
3. Click "Bottom-Left".
4. Observe that the Snackbar is full width.

Context

This bug is especially a problem when there are more than 8 or 9 words in the message, along with an action, and the snackbar looks oddly tall.

Your Environment

Tech	Version
Material-UI	v1.0.0-beta.15
React	v16.0.0
browser	Chrome

[oliviertassinari]

top center is broken too.

[mattd]

Woot! Thanks, @oliviertassinari! I appreciate the super quick fix.

[keatz55]

Getting the same for Material-UI v0.20.0

[shilangyu]

Im sorry, did they style guides change? It seems that snackbars no longer go full width on mobile but stay the same