It is an interesting feature, but maybe it should be applied only for success notifications because in the case of error notifications, some users (including myself) prefer to have the message on the screen for a longer time. An use case is when you bulk edit issues and you have errors for some issues and you will use the error message to resolve each issue one at a time.

Anyway, a feature related to this one is to add the possibility to close/hide the notification messages.
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The animation length can also be expanded by changing time in the place where it's called in *animation: slideFlash 3s ease-in-out forwards;* line and if we only want success messages to animate like that, then we can just move the animation call from a more global *div.flash* container to a *div.flash.notice* which represents only success messages. :)

Then there are also *div.flash.warning* and *div.flash.error* classes.
Maybe we could also just define different animation length for each of them, else if we want them to remain static, we can just skip adding any animation calls to them.
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Made improvements to this:
1. Now only animates on success notifications.
2. I made animation code more compact, because now animation will only do the collapse animation, so notification will appear as before, only it will collapse after 3 seconds, I also thought it's better like that, since it also moves #main container and it will be less annoying when done only once, which is now on it's collapsing.
3. I did minor tricks to make it work in IE11 like everywhere else.

previous patch must be reverted.
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