feat(ui): add a dropdown animation

ui/src/Components/Animations/DropdownSlide/index.css

@@ -0,0 +1,33 @@
+.components-animation-slide-enter,
+.components-animation-slide-appear {
+  opacity: 0.01;
+  overflow: hidden;
+  max-height: 0px;
+  border: 0;
+  padding: 0;
+  margin: 0;
+}
+.components-animation-slide-enter-active,
+.components-animation-slide-appear-active {
+  max-height: 500px; /* can't use auto here */
+  opacity: 1;
+  transition-property: max-height, opacity;
+  transition-duration: 0.15s;
+  transition-timing-function: ease-out;
+}
+
+.components-animation-slide-exit {
+  max-height: 500px; /* can't use auto here */
+  opacity: 1;
+}
+.components-animation-slide-exit-active {
+  opacity: 0.01;
+  overflow: hidden;
+  max-height: 0px;
+  border: 0;
+  padding: 0;
+  margin: 0;
+  transition-property: max-height, opacity;
+  transition-duration: 0.15s;
+  transition-timing-function: ease-out;
+}

ui/src/Components/Animations/DropdownSlide/index.js

@@ -0,0 +1,24 @@
+import React from "react";
+import PropTypes from "prop-types";
+
+import { CSSTransition } from "react-transition-group";
+
+import "./index.css";
+
+const DropdownSlide = ({ children, duration, ...props }) => (
+  <CSSTransition
+    in={true}
+    classNames="components-animation-slide"
+    timeout={150}
+    appear={true}
+    exit={true}
+    {...props}
+  >
+    {children}
+  </CSSTransition>
+);
+DropdownSlide.propTypes = {
+  children: PropTypes.node.isRequired
+};
+
+export { DropdownSlide };