fold("Content") { isExpanded = true style { paddingLeft = 0 startMargin = 0.px } fitToParentSize() hbox { style { paddingLeft = 0 startMargin = 0.px } drawer { item("Project structure") { expanded = true treeview<ProjectDir> { ..... more stuff here ... } } this += find<FileViewer>() { fitToParentSize() } } }