clj.cljc

      (dom/div
        (let [!cs (atom [0 1 2 3 4]) cs (e/watch !cs)]
          (e/for [c cs]
            (ui/button
                (e/fn [] (reset! !cs (vec (remove #{c} cs))))
              (dom/props {:class "fade-in"})
              (dom/text "REMOVE " c)))
          (ui/button
              (e/fn [] (swap! !cs conj (inc (peek cs))))
            (dom/text "ADD"))))

css.css

@keyframes fade-in {
    0% { opacity: 0; }
    100% { opacity: 1;}
}
.fade-in {
    animation: fade-in .5s;
}