toCssString = (declarations,  selectors,  conditions) => (
	`${conditions.map((condition) => `${condition}{`).join('')}${selectors.length ? `${selectors.join(',')}{` : ''}${declarations.join(';')}${selectors.length ? `}` : ''}${Array(conditions.length ? conditions.length + 1 : 0).join('}')}`
)
CSS right-hand side value, which may be a specially-formatted custom property.