src/vs/editor/browser/editorDom.ts/RefCountedCssRule/getCssText
class RefCountedCssRule:	private getCssText(className: string, properties: CssProperties): string {
		let str = `.${className} {`;
		for (const prop in properties) {
			const value = (properties as any)[prop] as string | ThemeColor;
			let cssValue;
			if (typeof value === 'object') {
				cssValue = `var(${asCssVariableName(value.id)})`;
			} else {
				cssValue = value;
			}

			const cssPropName = camelToDashes(prop);
			str += `\n\t${cssPropName}: ${cssValue};`;
		}
		str += `\n}`;
		return str;
	}