katana.sass

$m: 15px
$col: 12

*
  box-sizing: border-box

.main
  display: flex
  flex-flow: row wrap
  width: 94%
  margin: 0 auto

@for $i from 1 through $col
  .col-#{$i}
    width: calc(#{1 / $i}% - #{$m})
    margin: 0 0 0 $m

.fluid
  flex: 2
  margin: 0 0 0 $m

.clear
  width: 100%

@media (max-width: 600px)
  .main, .main > *
    width: 94% !important

  img
    max-width: 100%
    height: auto