igroot/lib/back-top/style/responsive.less

An React-based implementation

@media screen and (max-width: @screen-md) {
  .@{backtop-prefix-cls} {
    right: 60px;
  }
}

@media screen and (max-width: @screen-xs) {
  .@{backtop-prefix-cls} {
    right: 20px;
  }
}