Adding scroll bar to handle overflow of long network lists (#12706)

* Adding scroll bar to handle overflow of long network lists

* set scroll property to auto

* Add margin below scrollable network list

ui/components/app/dropdowns/network-dropdown.js

@@ -338,6 +338,8 @@ class NetworkDropdown extends Component {
             </div>
           ) : null}
         </div>
+
+        <div className="network-dropdown-list">
           {this.renderNetworkEntry('mainnet')}
 
           {this.renderCustomRpcList(rpcListDetail, this.props.provider)}
@@ -353,6 +355,7 @@ class NetworkDropdown extends Component {
             {this.renderNetworkEntry('goerli')}
             {this.renderNetworkEntry('localhost')}
           </div>
+        </div>
 
         {this.renderAddCustomButton()}
       </Dropdown>

ui/css/itcss/components/network.scss

@@ -128,6 +128,12 @@
   width: 100%;
 }
 
+.network-dropdown-list {
+  max-height: 330px;
+  overflow-y: auto;
+  margin-bottom: 8px;
+}
+
 .network-dropdown-divider {
   width: 100%;
   height: 1px;