12 Column, Mobile First Grid System

grid.css

* {
    box-sizing: border-box;
}

/*
 * 12 Column, Mobile First Grid System
 */

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

/* mobile columns */
[class*="col-"] {
    width: 100%;
}

/* tablet columns: */
@media only screen and (min-width: 600px) {
    [class*="col-"] {
        float: left;
        padding: 15px;
    }

    [class*="span-col"]:after {
        content: "";
    }

    .col-m-1 {width: 8.33%;}
    .col-m-2 {width: 16.66%;}
    .col-m-3 {width: 25%;}
    .col-m-4 {width: 33.33%;}
    .col-m-5 {width: 41.66%;}
    .col-m-6 {width: 50%;}
    .col-m-7 {width: 58.33%;}
    .col-m-8 {width: 66.66%;}
    .col-m-9 {width: 75%;}
    .col-m-10 {width: 83.33%;}
    .col-m-11 {width: 91.66%;}
    .col-m-12 {width: 100%;}

    .span-col-m-left-1 {margin-left: 8.33%;}
    .span-col-m-left-2 {margin-left: 16.66%;}
    .span-col-m-left-3 {margin-left: 25%;}
    .span-col-m-left-4 {margin-left: 33.33%;}
    .span-col-m-left-5 {margin-left: 41.66%;}
    .span-col-m-left-6 {margin-left: 50%;}
    .span-col-m-left-7 {margin-left: 58.33%;}
    .span-col-m-left-8 {margin-left: 66.66%;}
    .span-col-m-left-9 {margin-left: 75%;}
    .span-col-m-left-10 {margin-left: 83.33%;}
    .span-col-m-left-11 {margin-left: 91.66%;}
    .span-col-m-left-12 {margin-left: 100%;}

    .span-col-m-right-1 {margin-right: 8.33%;}
    .span-col-m-right-2 {margin-right: 16.66%;}
    .span-col-m-right-3 {margin-right: 25%;}
    .span-col-m-right-4 {margin-right: 33.33%;}
    .span-col-m-right-5 {margin-right: 41.66%;}
    .span-col-m-right-6 {margin-right: 50%;}
    .span-col-m-right-7 {margin-right: 58.33%;}
    .span-col-m-right-8 {margin-right: 66.66%;}
    .span-col-m-right-9 {margin-right: 75%;}
    .span-col-m-right-10 {margin-right: 83.33%;}
    .span-col-m-right-11 {margin-right: 91.66%;}
    .span-col-m-right-12 {margin-right: 100%;}
}

/* desktop columns */
@media only screen and (min-width: 768px) {
    [class*="col-"] {
        float: left;
        padding: 15px;
    }

    [class*="span-col"]:after {
        content: "";
    }

    .col-1 {width: 8.33%;}
    .col-2 {width: 16.66%;}
    .col-3 {width: 25%;}
    .col-4 {width: 33.33%;}
    .col-5 {width: 41.66%;}
    .col-6 {width: 50%;}
    .col-7 {width: 58.33%;}
    .col-8 {width: 66.66%;}
    .col-9 {width: 75%;}
    .col-10 {width: 83.33%;}
    .col-11 {width: 91.66%;}
    .col-12 {width: 100%;}

    .span-col-left-1 {margin-left: 8.33%;}
    .span-col-left-2 {margin-left: 16.66%;}
    .span-col-left-3 {margin-left: 25%;}
    .span-col-left-4 {margin-left: 33.33%;}
    .span-col-left-5 {margin-left: 41.66%;}
    .span-col-left-6 {margin-left: 50%;}
    .span-col-left-7 {margin-left: 58.33%;}
    .span-col-left-8 {margin-left: 66.66%;}
    .span-col-left-9 {margin-left: 75%;}
    .span-col-left-10 {margin-left: 83.33%;}
    .span-col-left-11 {margin-left: 91.66%;}
    .span-col-left-12 {margin-left: 100%;}

    .span-col-right-1 {margin-right: 8.33%;}
    .span-col-right-2 {margin-right: 16.66%;}
    .span-col-right-3 {margin-right: 25%;}
    .span-col-right-4 {margin-right: 33.33%;}
    .span-col-right-5 {margin-right: 41.66%;}
    .span-col-right-6 {margin-right: 50%;}
    .span-col-right-7 {margin-right: 58.33%;}
    .span-col-right-8 {margin-right: 66.66%;}
    .span-col-right-9 {margin-right: 75%;}
    .span-col-right-10 {margin-right: 83.33%;}
    .span-col-riGght-11 {margin-right: 91.66%;}
    .span-col-right-12 {margin-right: 100%;}
}

.col-text-right {
  text-align: right;
}

.col-text-center {
  text-align: center;
}

/* End of 12 Column, Mobile First Grid System */

JS Bin is here: https://jsbin.com/jibodeyuxa/edit?html,css