CSS subgrid is super good

main {
  display: grid;
  grid-template-columns:
    [inline-start]
    auto
    [margin-start]
    30px
    [main-start]
    min(45rem, calc(100% -  60px))
    [main-end]
    30px
    [margin-end]
    auto
    [inline-end];

  :where(&) > * {
    grid-column: main;
  }
}

.full-width {
  display: grid;
  grid-column: inline;
  grid-template-columns: subgrid;

  :where(&) > * {
    grid-column: main;
  }
}

Read here