src/vs/base/browser/ui/inputbox/inputBox.ts/InputBox/applyStyles
class InputBox:	protected applyStyles(): void {
		const styles = this.options.inputBoxStyles;

		const background = styles.inputBackground ?? '';
		const foreground = styles.inputForeground ?? '';
		const border = styles.inputBorder ?? '';

		this.element.style.backgroundColor = background;
		this.element.style.color = foreground;
		this.input.style.backgroundColor = 'inherit';
		this.input.style.color = foreground;

		// there's always a border, even if the color is not set.
		this.element.style.border = `1px solid ${dom.asCssValueWithDefault(border, 'transparent')}`;
	}