Scroll only the occupants list in the sidebar.

css/converse.css

@@ -2317,15 +2317,11 @@
         float: right;
         vertical-align: top;
         background-color: white;
-        overflow: scroll;
         border-left: 1px solid #818479;
         border-bottom-right-radius: 4px;
         width: 30%;
         height: 100%;
         padding: 0.5em; }
-        #converse-embedded-chat .chatroom .box-flyout .chatroom-body .occupants.hidden,
-        #conversejs .chatroom .box-flyout .chatroom-body .occupants.hidden {
-          display: none; }
         #converse-embedded-chat .chatroom .box-flyout .chatroom-body .occupants .occupants-heading,
         #conversejs .chatroom .box-flyout .chatroom-body .occupants .occupants-heading {
           padding: 0.3em 0;
@@ -2336,6 +2332,11 @@
           overflow-x: hidden;
           overflow-y: auto;
           list-style: none; }
+          #converse-embedded-chat .chatroom .box-flyout .chatroom-body .occupants ul.occupant-list,
+          #conversejs .chatroom .box-flyout .chatroom-body .occupants ul.occupant-list {
+            overflow-y: scroll;
+            height: -webkit-calc(100% - 200px);
+            height: calc(100% - 200px); }
           #converse-embedded-chat .chatroom .box-flyout .chatroom-body .occupants ul li,
           #conversejs .chatroom .box-flyout .chatroom-body .occupants ul li {
             cursor: default;

sass/_chatrooms.scss

@@ -93,15 +93,11 @@
                     float: right;
                     vertical-align: top;
                     background-color: white;
-                    overflow: scroll;
                     border-left: 1px solid $text-color;
                     border-bottom-right-radius: $chatbox-border-radius;
                     width: 30%;
                     height: 100%;
                     padding: 0.5em;
-                    &.hidden {
-                        display: none;
-                    }
                     .occupants-heading {
                         padding: 0.3em 0;
                         font-weight: bold;
@@ -111,6 +107,12 @@
                         overflow-x: hidden;
                         overflow-y: auto;
                         list-style: none;
+
+                        &.occupant-list {
+                            overflow-y: scroll;
+                            @include calc(height, '100% - 200px');
+                        }
+
                         li {
                             cursor: default;
                             display: block;