Make the "Copied!" notification visible again

It was made invisible in 2f07551,
because the notification was located outside the `.copy-controls`,
and anything outside it was hidden to prevent long mask addresses
from breaking the layout.

Thus, with this change, I've simply moved the notification to
overlap the copy button and be positioned in the middle of it.

frontend/src/components/dashboard/aliases/Alias.module.scss

@@ -95,16 +95,14 @@ $toggleTransitionDuration: 200ms;
     background-color: $color-violet-30;
     color: $color-white;
     border-radius: $border-radius-md;
-    padding: $spacing-xs;
+    padding: 0 $spacing-xs;
     // By allowing this to overlap other elements,
     // we don't need to reserve empty space for it.
     // Otherwise, this empty space would push the
     // .expand-toggle out of the card on small screens:
     position: absolute;
-    left: 50%;
+    left: $spacing-xs;
     top: 0;
-    // right: 0;
-    transform: translateX(-50%) translateY(-100%);
 
     &.is-shown {
       pointer-events: auto;