Edit in JSFiddle

* {
    //margin: 0;
    box-sizing: border-box;
}
body {
    font-family: "Helvetica Neue";
    font-weight: 200;
    background-color: #ddd;
}
.grid {
    padding: 0.5em;
    max-width: 968px;
    min-width: 300px;
    //position: relative;
    margin: 0 auto;
    background-color: white;
}
$width = 2px;
.grid header {
    width: 100%;
    font-weight: 400;
    margin-bottom: 4px;
    .day {
        background-color: #333;
        color: #ddd;
        //outline: 2px solid white;
    }
}
.grid section, .grid header {
    margin: 0 0 0.5%;
    padding: 0;
}
/*.grid header::nth-child(odd) {
    margin-right: 5px;
}*/
.day {
    background-color: #ebebeb;
    //background-color: #e6e6e6;
    //display: inline-block;
    float: left;
    width: 18px;
    width: 13.8571%;
    //width: calc('14.2857% - #{$width}');
    //width: calc('(100% - #{6 * $width}) / 7');
    padding: 1.8em 0 2em;
    margin: 0;
    text-align: center;
    //border-bottom: 2px solid white;
    position: relative;
    //margin-right: $width;
    margin-right: 0.5%;
    &:last-child {
        margin-right: 0;
    }
}
.events {
    //padding: 1.25em 0;
    //color: #278ed3;
    font-weight: 400;
}
.event-number {
    position: absolute;
    left: 0;
    right: 0;
    line-height: 0.5;
}
.event-bullet {
    display: none;
    position: absolute;
    left: 0;
    right: 0;
    line-height: 0.5;
}
.day.events div {
    //text-decoration: underline;
}
section .day {
    //outline-right: 2px solid white;
    //outline: 2px solid white;
}

.grid .day:empty {
    border: none;
    background-color: rgba(0,0,0,0);
    //outline: none;
}

.clearfix{
    *zoom:1;
}
.clearfix:before,.clearfix:after{
    display:table;
    content:" ";
    //line-height:0;
}
.clearfix:after{
    clear:both;
}

@media all and (max-width: 600px) {
    .events .event-number {
        display: none;
    }
    .events .event-bullet {
        display: block;
    }
    .days {
        padding: 1.8em 0;
    }
    body {
        //background-color: purple;
    }
}

@media all and (max-width: 480px) and (min-width: 320px) {
    body {
        //background-color: red;
    }
    .day.events, .day {
        padding: 1.2em 0;
    }
}

@media all and (max-width: 320px) {
    body {
        //background-color: blue;
    }
    .day.events {
        padding: 0.75em 0;
    }
    .event-bullet {
        line-height: 0.5;
    }
    .grid .day {
        padding: 1em 0;
    }
}