UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36

Steps to reproduce the problem:
1. go to https://codepen.io/qbolec/pen/QMERdK
2. observe the width of <input> by comparing its red border with blue border of its parent

What is the expected behavior?
I've expected that when setting `{left:0; right:0; position:absolute}` the width of the input should be equal to parent's width (perhaps minus padding, or margins or whatever) so it should be at most 40px.

What went wrong?
The input has width of 125px.
Adding `input {width: 100%}` makes it behave as I expected.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 59.0.3071.115  Channel: n/a
OS Version: OS X 10.12.5
Flash Version: 

I've tested this in Firefox, and in Firefox not only the width is "wrong" but also the height is too small.

In Safari it looks exactly as I would expect, that is the input is contained in the div.