For player-container and player-list-container, I think it's better to use percentage instead of all absolute rem. According to page 13 of the spec, looks like for the width of player-container should keep (16.6 x 5) 83rem and for player-list-container is (3 + 45 + 3) 45rem, so I guess to give 83rem for player-list-container and (100% - 83rem) for player-container, or (100% - 45rem) for player-list-container and 45rem for player-container will be a safer choice.