Hello @unifiedcomms ,
The certificates aren't expired for our Knowledge Base article library. I'd advise going through connectivity troubleshooting if you're having issues connecting with our Help resources, as that will likely lead to having issues with our main site as well down the line. Since you're having issues viewing the KB, then I'd advise checking out our Connectivity Troubleshooting FAQ here in the Community.
There isn't a "required size" for custom backgrounds. Per our article on preparing images for upload, we compress any image that's over 1200 pixels wide, and the image's height is reduced proportionally. There are different options for how you want your outer background to appear, whether that's centered, filled, or tiled.
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