Zelenin\yii\SemanticUI\widgets\ActiveField::registerStyles PHP Method

    public function registerStyles()
    {
        $classNamesToSelectors = function ($classNames) {
            return '.' . implode('.', preg_split('/\\s+/', $classNames, -1, PREG_SPLIT_NO_EMPTY));
        };
        $this->form->getView()->registerCss('
        ' . $classNamesToSelectors($this->errorOptions['class']) . ' {
            display: none;
        }
        ' . $classNamesToSelectors($this->form->errorCssClass) . ' ' . $classNamesToSelectors($this->errorOptions['class']) . ' {
            display: inline-block;
        }
        ');
    }