papercss/src/layout/_flexbox.scss

$number-columns: 12;

@mixin create-flex-classes($colName, $breakpoint: 0) {
  @include resp($min: $breakpoint) {
    @for $i from 1 through $number-columns {
      .#{$colName}-#{$i} {
        flex: 0 0 $i * 100% / $number-columns;
        max-width: $i * 100% / $number-columns;
      }
    }
  }
}

.row {
  display: flex;
  flex-flow: row wrap;
  margin-bottom: 1rem;
  margin-left: auto;
  margin-right: auto;

  &.flex-right {
    justify-content: flex-end;
  }

  &.flex-center {
    justify-content: center;
  }

  &.flex-edges {
    justify-content: space-between;
  }

  &.flex-spaces {
    justify-content: space-around;
  }

  &.flex-top {
    align-items: flex-start;
  }

  &.flex-middle {
    align-items: center;
  }

  &.flex-bottom {
    align-items: flex-end;
  }
}

.col {
  padding: 1rem;

  @include resp(sm) {
    @include col-size(100%);
  }
}

.col-fill {
  flex: 1 1 0;
  width: auto;
}

@include create-flex-classes(col);
@include create-flex-classes(xs, $xsmall-screen);
@include create-flex-classes(sm, $small-screen);
@include create-flex-classes(md, $medium-screen);
@include create-flex-classes(lg, $large-screen);

.align-top {
  align-self: flex-start;
}

.align-middle {
  align-self: center;
}

.align-bottom {
  align-self: flex-end;
}

.container {
  margin: 0 auto;
  max-width: 960px;
  position: relative;
  width: 100%;

  @include resp(md) {
    width: 85%;
  }
  @include resp(xs) {
    width: 90%;
  }
}