99 animated Steam profile backgrounds where red is the main colour, ranked by community votes. All of them are sold in the Steam Points Shop.
Almost all animated profile backgrounds cost 2,000 Steam Points. Points are earned by buying games and content on Steam (100 points per US dollar spent) and by receiving awards.
No. Animated backgrounds are sold only in the Steam Points Shop and can't be traded or sold.
After buying it in the Points Shop, open your profile, click Edit Profile → Profile Background, choose the animated background and save.
Steam shows a still image when animations are turned off in your Steam settings or when the client limits animations to save resources. Visitors with animations on still see it move.