Limiting the width of Wikipedia-articles when reading on widescreens

I’m using a widescreen display most of the day, which makes it quite useful to have two browser windows openĀ or one browser window and a text-editor side-by-side. But sometimes I keep the browser window maximized, which is a bad thing for sites like Wikipedia. The articles get dragged out in full width, making the lines a bit too long to read comfortably:

Way too long lines to read comfortably.
Way too long lines to read comfortably.

Thankfully, it is quite easy to fix this. I came over one solution with a bookmarklet, but this requires you to click a button for each article. If you have logged in to Wikipedia, however, you may add your own custom CSS that will appear on all articles by clicking Preferences > Appearance > Custom CSS.

In the editor that shows up, add the following:

body {
    max-width: 65em;
    margin-left: auto;
    margin-right: auto;
    position: relative;
    float: none;

After this change, Wikipedia pages are limited to the width of 65em (approximately 1000 px):

Wikipedia with a much better width.
Wikipedia with a much better width.

If you want to add this to all pages on the web, you should consider a bookmarklet like the one mentioned here.