Here’s a twitter template with an example of my current (as of date) background as an example. Inside of the template I made guides that match up with the content areas. This .psd is designed for 1600 pixel width monitor display in mind; however, there I pointed out the sliver that is always present as well.
The main twitter content slides back & forth depending on your monitor/resolution, so it’s up to you where you feel comfortable adding extra content that people may or may-not see.
Also when designing your background, you can put elements to the far right but be aware that many users will not see them depending on what monitor/resolution they’re using again. As stated above, with the guides I included a ‘twitter content area’ (where your tweets are housed) in its actual size. So you can move it into different positions for other monitors. Just keep in mind what other users will see.
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