How easy responsive design can be with Sass

layout.sass

#content-wrapper
  +container

  #about

    // Default (smallest screens)
    +column(100%)
    background-color: #ccc

    // Respond to other screen widths
    +respond-to(tablet)
      width: 33.333%

    +respond-to(desktop)
      width: 25%

  #primary-content
    +column(100%)

    +respond-to(tablet)
      width: 66.666%

    +respond-to(desktop)
      width: 50%

  #secondary-content
    +column(100%)
    display: none

    +respond-to(desktop)
      width: 25%
      display: block