Very simple 12-column grid system in scss

grid.scss

$small: 320px;

*[class^="col-"]{
    float: left;
    box-sizing: border-box;
    @media only screen and (max-width: $small) {
        &.not-for-small{
            width: 100%;
            float: none
        }
    }
}

@for $i from 1 through 12 {
    .col-#{$i}{
        width: $i * 100% / 12;
    }
}

@for $i from 1 through 12 {
    .skip-#{$i}{
        margin-left: $i * 100% / 12;
    }
}

.row:after{
    content: " ";
    display: block;
    clear: both
}