element-ui/packages/theme-chalk/src/main.scss

@import "mixins/mixins";
@import "common/var";
@include b(main) {
  // IE11 supports the <main> element partially https://caniuse.com/#search=main
  display: block;
  flex: 1;
  flex-basis: auto;
  overflow: auto;
  box-sizing: border-box;
  padding: $--main-padding;
}