src/vs/workbench/browser/parts/editor/tabsTitleControl.ts/TabsTitleControl/redrawTabBorders
class TabsTitleControl:	private redrawTabBorders(index: number, tabContainer: HTMLElement): void {
		const isTabSticky = this.group.isSticky(index);
		const isTabLastSticky = isTabSticky && this.group.stickyCount === index + 1;

		// Borders / Outline
		const borderRightColor = ((isTabLastSticky ? this.getColor(TAB_LAST_PINNED_BORDER) : undefined) || this.getColor(TAB_BORDER) || this.getColor(contrastBorder));
		tabContainer.style.borderRight = borderRightColor ? `1px solid ${borderRightColor}` : '';
		tabContainer.style.outlineColor = this.getColor(activeContrastBorder) || '';
	}