react-misc-toolbox/dist/_modal.scss

.modal {
  &__background {
    position: fixed;
    height: 100%;
    top: 0;
    left: 0;
    width: 100%;

    z-index: 4;
    opacity: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    -webkit-tap-highlight-color: transparent;
  }
}