Say 又 (yòu) twice to connect two adjectives that are either both positive or both negative.
她的头发又黑又好看。
Tā de tóufǎ yòu hēi yòu hǎokàn.
Her hair is both black and nice.
这个苹果又大又好吃。
Zhè ge píngguǒ yòu dà yòu hàochī.
This apple is both big and tasty.
我的猫又饿又累。
Wǒ de māo yòu è yòu lèi.
My cat is both hungry and tired.