src/vs/editor/contrib/zoneWidget/zoneWidget.ts/Arrow/_updateStyle
class Arrow:	private _updateStyle(): void {
		dom.removeCSSRulesContainingSelector(this._ruleName);
		dom.createCSSRule(
			`.monaco-editor ${this._ruleName}`,
			`border-style: solid; border-color: transparent; border-bottom-color: ${this._color}; border-width: ${this._height}px; bottom: -${this._height}px; margin-left: -${this._height}px; `
		);
	}