Custom checkbox changing position on click

I think I am missing something but I can't find a solution to the following problem.

I am using custom checkboxes on a list of sentences. At first it looks good but once you check the first checkbox, it moves. I can't find out why the checkboxes move once you check them?

Here is a fiddle: http://ift.tt/2ezGh5p
I have noticed that by changing content: "/2714"; to content: ""; the checkbox doesn't move on click.

Can't understand how the content affects the position of the checkbox.

In other questions I saw recommendations to use vertical-align:middle, it doesn't work for me.

Any ideas?