Twenty Fifteen: Images in the editor still overflow in some cases

[iamtakashi]

Since [31849], the images in the editor are better in small screens but the change doesn't seem to take account the margin in the editor: 40px on each side. Therefore when the editor is say, 668px wide, an image overflows. I think the max-width for the media query should be 740px (660 + 40 + 40)px.

Before: (Note the horizontal scroll bar and the box model view)

After:

Related: #31250, #31253

[iamtakashi]

If this looks good to go I'll make a patch for Twenty Fourteen too.

[lancewillett]

Good to go from looking at the patch in terms of the CSS itself, just testing a bit more for the breakpoint.

[lancewillett]

Looks good in testing.

[lancewillett]

In 32090:

Twenty Fifteen: update editor styles to better account for adaptive images in small screens.

See #31934, props iamtakashi.

[lancewillett]

@iamtakashi Feel free to put Twenty Fourteen patch here on the same ticket if you want to.

[iamtakashi]

For Twenty Fourteen.

[lancewillett]

In 32094:

Twenty Fourteen: update editor styles to better account for adaptive images in small screens.

Fixes #31934, props iamtakashi.