Markdown editor expands to whole screen width

[markuskonojacki]

For Bug Reports

After upgrade from v0.18.0 to:

• BookStack Version: v0.18.3
• PHP Version: 7.1.10-1+020170929170631.9+jessie1.gbp501135 (cli) (built: Sep 29 2017 17:33:58) ( NTS )
• MySQL Version: mysql Ver 14.14 Distrib 5.5.57, for debian-linux-gnu (x86_64) using readline 6.3

Expected Behavior

A limited maximal width of the markdown editor.

Current Behavior

The markdown editor expands until it spans the whole screen width. Thus hiding the preview as well as the right sidebar. The problem is new after an upgrade from v0.18.0 to v0.18.3.

Steps to Reproduce

Couldn't reproduce this in IE 11, only in Chrome. But on different computers in Chrome and after clearing the cache. I've not tried any other browser.

Maybe related to #502

Custom HTML header from the gif (removing doesn't help):

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.30.0/theme/vibrant-ink.min.css"/>
<script>window.codeTheme='vibrant-ink';</script>

<link href="https://fonts.googleapis.com/css?family=Lato" rel="stylesheet">
<style>
body, button, input, select, label, textarea {
  font-family: 'Lato', sans-serif;
}
.Codemirror, pre, #markdown-editor-input, .editor-toolbar, .code-base {
  font-family: monospace;
}
</style>