During a review, I've found a number of visual issues with warning messages:

• Use fade out transition to make banner disappear. It should slide up when showing (it does, currently), then fade out if closed.
• Don't show an empty line between the title and the second line of text. Instead, show the two lines directly one after the other.
• Only show at most two lines of text: the title plus a single line below. Let the browser abbreviate the line, if it becomes too long.
• Add a white space character between "Info:" prefix and the message title.
• Align close button of banner with close button of apps.