In our latest update we have modified hook names and function names adhering to WordPress standards. If you have customized the theme or created child theme, please go through following points and see if any case is applicable.
if you are using hook with prefix cyberchimps replace it with responsive eg. Replace cyberchimps_sanitize_hex with responsive_sanitize_hex
If you are overriding existing templates of responsive theme which has function get_responsive_breadcrumb_lists replace this function name responsive_breadcrumb_lists
The sidebar has not disappeared but is not visible since there are no widgets added in the sidebar. To display a sidebar, simply go to Appearance > Widgets and add widgets to your desired sidebar.
Earlier, as per old design, if there were no widgets added in sidebar, Archives was visible in the sidebar.
Users of Responsive Theme can add custom CSS. To add custom CSS please follow Customize > Additional CSS.
Here you can add custom CSS. You can preview the changes and publish it.
Users of Responsive Pro Theme can minify CSS which can help speed up your website. To minify CSS please follow Customize > Theme Options > Theme Elements > Enable minified css? Check the provided checkbox to minify CSS.