src/vs/base/browser/ui/button/button.ts/Button/updateBackground
class Button:	private updateBackground(hover: boolean): void {
		let background;
		if (this.options.secondary) {
			background = hover ? this.options.buttonSecondaryHoverBackground : this.options.buttonSecondaryBackground;
		} else {
			background = hover ? this.options.buttonHoverBackground : this.options.buttonBackground;
		}
		if (background) {
			this._element.style.backgroundColor = background;
		}
	}