.calendar {
  margin: 4rem;
  padding: 0;
  list-style: none;
  font-size: 1.4rem;
}

.calendar-day {
  color: #fff;
  position: relative;
  box-sizing: border-box;
}

.calendar-day:nth-child(7n+1)::before {
  content: attr(data-week);
  position: absolute;
  color: #999;
}

.calendar-day::after {
  content: attr(data-weekday);
  position: absolute;
  color: #999;
}

.calendar-day__content {
  background: #4e8792;
}

.calendar-day--not-month .calendar-day__content {
  opacity: .5;
}

.calendar-day--today .calendar-day__content {
  background-color: #67c77c;
}

.calendar-day--entry .calendar-day__content {
  background-color: #ab6381;
}

.calendar-day__number {
  position: absolute;
  top: .5rem;
  left: .5rem;
}

@media screen and (max-width: 40rem) {
  .calendar-day {
    margin: 0 0 2px;
  }

  .calendar-day:nth-child(7n+1)::before {
    left: 0;
    right: 0;
    bottom: calc(100% + .5rem);
    display: block;
    text-align: center;
  }

  .calendar-day::after {
    right: calc(100% + .5rem);
    top: .5rem;
  }

  .calendar-day--not-month {
    display: none;
  }

  .calendar-day--begin-week {
    margin-top: 3rem;
  }

  .calendar-day__content {
    padding: 0 0 20%;
  }
}

@media screen and (min-width: 40rem) {
  .calendar {
    display: flex;
    flex-wrap: wrap;
  }

  .calendar-day {
    flex-basis: calc(14.28571% - 2px);
    margin: 1px;
  }

  .calendar-day:nth-child(7n+1)::before {
    right: calc(100% + .5rem);
    top: .5rem;
  }

  .calendar-day::after {
    display: none;
  }

  .calendar-day:nth-child(-n+7)::after {
    display: inline;
    bottom: calc(100% + .2rem);
    left: .5rem;
  }

  .calendar-day--not-month {
    display: block;
  }

  .calendar-day--past .calendar-day__number {
    opacity: .5;
  }

  .calendar-day__content {
    padding-bottom: 100%;
  }
}