CSS problem in editor screen

[Milmor]

Hello,
today i upgraded my WordPress from v. 3.9 beta1 to beta3 and i noticed that in the editor screen if i add some text the preview isn't using the 100% of the available width.

The file editor-style.css looks like to cause this problem:

html .mceContentBody {
	font-size: 100%;
	max-width: 474px;
}

I've attached a screen.
Regards

[Milmor]

preview of css bug

[jesin]

Hi Milmor,

You have found the right piece of code causing this problem but this code exists in the TwentyFourteen theme and not the WordPress core.

Check out this file - twentyfourteen/css/editor-style.css

Try out a different theme.

I am able to reproduce this problem even on WordPress 3.8.1 with TwentyFourteen.

[SergeyBiryukov]

i noticed that in the editor screen if i add some text the preview isn't using the 100% of the available width.

It's not supposed to. The width is controlled by the theme's editor-style.css file:
tags/3.8.1/src/wp-content/themes/twentyfourteen/css/editor-style.css#L22​.

The idea is to achieve the same look as on front-end, see #11512. Related: #21536.