Ext JS 'fieldset' : Can not reduce space between title and it's border inside 'Ext.Window'

Question

me.customfieldstatepopup = new Ext.Window({
            title: eAkte.Locale.i18n.label('save_state_custom_field'),
            cls: 'customfieldstatepopup',
            closeAction: 'destroy',
            modal: true,
            width: 520,
            items: [
              {
                xtype: 'container',
                layout: 'hbox',
                padding: 10,
                items: [{
                    xtype: 'fieldset',
                    title: eAkte.Locale.i18n.label('save_state_custom_field_visible'),
                    flex: 1,
                    //margin: 0,
                    items: [{
                        xtype: 'treepanel',
                        reference: 'visibleFieldTree',
                        itemId: 'visibleFieldTree',
                        width: 220,
                        height: 200,
                        rootVisible: false,
                        hideHeaders: true,
                        multiSelect: true,
                        viewConfig: {
                            plugins: {
                                ptype: 'treeviewdragdrop',
                                ddGroup: 'custom-field-drag-drop',
                                allowContainerDrops: true
                            }
                        }
                    }]
                }, {
                    xtype: 'fieldset',
                    title: eAkte.Locale.i18n.label('save_state_custom_field_hidden'),
                    flex: 1,
                    margin: '0 0 0 20',
                    items: [{
                        xtype: 'treepanel',
                        itemId: 'hiddenFieldTree',
                        width: 220,
                        height: 200,
                        rootVisible: false,
                        hideHeaders: true,
                        multiSelect: true,
                        viewConfig: {
                            plugins: {
                                ptype: 'treeviewdragdrop',
                                ddGroup: 'custom-field-drag-drop',
                                allowContainerDrops: true
                            }
                        }
                    }]
                }]
            },
 );

here is my code for Ext JS window , inside that i have two fieldset elements, for both fieldset , top too much space after title and top line ,i want to remove extra space between line and title.

Reason behind problem is Ext.Window or should i change other property?

Current view

Expexted

I've placed width property at different places, but not woking