react中布局样式style.less中的calc不生效

去使用：css .modal_overlay {   position: fixed;   top: 0;   left: 0;   bottom:0;   z-index: 1000;   background-color:rgba(11,11,11,0.4);   width: 100%;   .modal {     position: fixed;     top: calc(100% –

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