src/vs/workbench/contrib/typeHierarchy/browser/typeHierarchyPeek.ts/TypeHierarchyTreePeekWidget/_applyTheme
class TypeHierarchyTreePeekWidget:	private _applyTheme(theme: IColorTheme) {
		const borderColor = theme.getColor(peekView.peekViewBorder) || Color.transparent;
		this.style({
			arrowColor: borderColor,
			frameColor: borderColor,
			headerBackgroundColor: theme.getColor(peekView.peekViewTitleBackground) || Color.transparent,
			primaryHeadingColor: theme.getColor(peekView.peekViewTitleForeground),
			secondaryHeadingColor: theme.getColor(peekView.peekViewTitleInfoForeground)
		});
	}