Redesign notification dismiss button

X wasn’t centering properly

ui/src/shared/components/Notification.js

@@ -66,9 +66,7 @@ class Notification extends Component {
           <div className="notification-message">
             {message}
           </div>
-          <button className="notification-close" onClick={this.handleDismiss}>
-            <span className="icon remove" />
-          </button>
+          <button className="notification-close" onClick={this.handleDismiss} />
         </div>
       </div>
     )

ui/src/style/theme/_notifications.scss

@@ -60,6 +60,24 @@ $notification-margin: 12px;
   transition:
     opacity 0.25s ease;
 
+  &:before,
+  &:after {
+    content: '';
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    width: 16px;
+    height: 2px;
+    border-radius: 1px;
+    background-color: $g20-white;
+  }
+  &:before {
+    transform: translate(-50%,-50%) rotate(-45deg);
+  }
+  &:after {
+    transform: translate(-50%,-50%) rotate(45deg);
+  }
+
   &:hover {
     cursor: pointer;
     opacity: 1;
@@ -108,6 +126,10 @@ $notification-margin: 12px;
   span.icon {
     color: $text-color;
   }
+  .notification-close:before,
+  .notification-close:after {
+    background-color: $text-color;
+  }
 }
 
 //  Alert Themes