Make Theme Selector responsive

As an Administrator navigate to the Theme Selector page. How this page is viewed is dependent on the theme setting 'Detect mobile devices'. If set to detect a mobile devices then the screen you see first is the one that shows Default, Laptop, Legacy, Mobile options when selecting a theme. So depending on which themes are in use, you will need to check that the screenshot.jpg image, in those whose device type is set, do not extend beyond the edge of the page. Next Click on the button marked 'Change theme' for the Default type; The page that opens is the same page if you do not have the Detect mobile devices. Float the browser window by clicking on the middle of the three icons in the top right-hand corner of your browser window. Pointing your mouse on the right edge of your browser window, you should then see a small double pointed arrow something like this: <--->. By LEFT clicking the arrow 'push' the screen towards the left and TEST to see how the page reforms in width, and that the screenshot images shrink in size, allowing the page to still look uniform even when in a narrow screen. Test that the images and page are consistent when scrolling up/down the page too. This behaviour should be true for all the other devices types.