Your .div and .divanimated selectors have the same specificity. Because the .div style is specified after the .divanimated selector it will override all the similar attributes such as animation-name.
For this example, you could fix the problem by adding the div class to the .divanimated selector.
Your new CSS selector (line 1 of your CSS) would be:
.div.divanimated
solved Start a Animation when I press a Button doesn’t work