Issue with Responsiveness

Hi,

Since update 3.1 I have had an issue with the responsiveness and CSS styling.

It only seems to be when the screen size is in the mid range. between 480 px to 1000 px. The sidebars seem to stay a fixed size pushing the center smaller. This is a problem until it reaches around mobile size 480px where it renders fine.

This is something to do with my child theme style.css. I renamed the file and once the cache was cleared it looks like the sidebars do not stay fixed without the child style.css and it renders ok all the way down to mobile.

https://www.dugswelcome.com/

Can someone advise what CSS is missing? I’m assuming I need to add in rules around screen resolution sizes possibily related to the below:

/* Tablet – 800px, 768px & 720px */
@media only screen

The issue has only come about due to the changes to css files for the latest theme updates and seemed to be ok when there was a responsive.css

screenshot here:
https://www.dropbox.com/s/vd6hcn01ea9iaiu/2016-04-18%2012_38_24-Dog%20Friendly%20Pubs%2C%20Cafes%2C%20Hotels%20%26%20Dog%20Walks%20_%20Dugs.png?dl=0