Fix layout of Preview container
Fix layout of Preview container

Make sure that the Preview container has a max width of 100% of its parent so
that stories it contains do not cause it to expand horizontally.

storybooks/storybook,storybooks/react-storybook,storybooks/react-storybook,storybooks/storybook,storybooks/storybook,kadirahq/react-storybook,storybooks/react-storybook,storybooks/storybook,storybooks/storybook,storybooks/storybook,storybooks/react-storybook,kadirahq/react-storybook,storybooks/storybook