Stop access token overflowing the box (#10069)

Use a scrollable div for the access token to stop it overflowing.

Author: sbjaj33

res/css/views/elements/_CopyableText.pcss

@@ -38,9 +38,12 @@ limitations under the License.
         cursor: pointer;
         margin-left: 20px;
         display: block;
+        /* If the copy button is used within a scrollable div, make it stick to the right while scrolling */
+        position: sticky;
+        right: 0;
         /* center to first line */
-        position: relative;
         top: 0.15em;
+        background-color: $background;
 
         &::before {
             content: "";

res/css/views/settings/tabs/user/_HelpUserSettingsTab.pcss

@@ -28,4 +28,9 @@ limitations under the License.
             margin-bottom: $spacing-16;
         }
     }
+
+    /* prevent the access token from overflowing the text box */
+    div .mx_CopyableText {
+        overflow: scroll;
+    }
 }