style.css

.calendar {
  position: relative;
  box-sizing: border-box;
  width: 240px;
}

.calendar * {
  box-sizing: border-box;
}

.calendar .calendar-item {
  display: flex;
  align-items: flex-start;
  height: 200px;
  display: flex;
  flex-wrap: wrap;
}

.calendar .calendar-action {
  width: 24px;
  height: 24px;
  text-align: center;
  border: none;
  position: absolute;
  top: 0;
  z-index: 100;
  font-size: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.calendar-action:before {
  content: "";
  display: block;
  width: 10px;
  height: 10px;
  border: 1px #06a2d0 solid;
  transform: rotate(45deg);
}
.calendar-action:hover:before {
  border-color: #047192;
}
.calendar-action.disabled:before {
  border-color: #ccc;
}
.calendar-action:hover:before {
  border-color: #ccc;
}

.calendar-action.prev:before {
  border-top: none;
  border-right: none;
  margin-left: 12px;
}
.calendar-action.next:before {
  border-left: none;
  border-bottom: none;
  margin-right: 12px;
}

.calendar .calendar-action:focus {
  outline: none;
}
.calendar .calendar-action.disabled {
  color: #ccc;
}
.calendar .calendar-action.prev {
  left: 0;
  float: left;
}
.calendar .calendar-action.next {
  right: 0;
  float: right;
}

.calendar .calendar-head,
.calendar .calendar-body,
.calendar .calendar-day {
  display: flex;
  flex-wrap: wrap;
  width: 100%;
}

.calendar .calendar-head {
  align-items: center;
  justify-content: center;
  height: 24px;
  position: relative;
  font-size: 12px;
}
.calendar .calendar-day {
  height: 24px;
}
.calendar .calendar-cell {
  font-size: 12px;
  width: 14.285714285714286%;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 24px;
  flex-direction: column;
}

.calendar .calendar-body .date {
  font-size: 12px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  display: flex;
  align-content: center;
  justify-content: center;
  align-items: center;
}

.calendar .calendar-cell:not(:empty) {
  cursor: pointer;
}
.calendar .calendar-cell ~ .calendar-cell.disabled {
  cursor: pointer;
}
.calendar .calendar-cell.disabled {
  color: #d6d6d6;
  cursor: default;
}
.calendar .calendar-cell.in-range .date {
  background: #999;
  color: white;
}
.calendar .calendar-cell.active {
  position: relative;
}
.calendar .calendar-cell.active .date {
  color: #fff;
  background: #06a2d0;
}

.calendar-title {
  font-size: 12px;
}

.calendar {
  width: 780px;
  display: flex;
  flex-wrap: wrap;
}
.calendar .calendar-item {
  width: 260px;
  padding-left: 20px;
}

.calendar .calendar-item:nth-of-type(3n) {
  border-right: none;
}

.display-value {
  font-size: 14px;
  padding: 12px;
  border-bottom: 1px #ccc solid;
}

.highlight {
  color: #06a2d0;
}
.calendar-cell.start-date .date {
  background: #f51 !important;
}
.calendar-cell.end-date .date {
  background: #f51 !important;
}
.calendar .calendar-cell.active .date {
  color: white;
  background-color: #f51;
}
#date-value {
  font-size: 14px;
  padding: 12px;
}
.is-weekday,
.is-weekend {
  color: #f51 !important;
}

.is-weekday.disabled,
.is-weekend.disabled {
  color: pink !important;
}

#container {
  border: 1px #ccc solid;
  width: 820px;
  padding: 20px;
}

.calendar .calendar-item {
  position: relative;
  /* border-top: 1px #ccc solid; */
}
.calendar .calendar-body {
  border-top: 1px #ccc solid;
  position: relative;
  border-bottom: 1px #ccc solid;
}
.calendar .calendar-item:after,
.calendar .calendar-item:before {
  content: "";
  display: block;
  width: 1px;
  position: absolute;
  top: 52px;
  left: 20px;
  bottom: 2px;
  background-color: #ccc;
}

.calendar .calendar-item:after {
  right: 0;
  left: auto;
  background-color: #ccc;
}
.calendar .calendar-cell {
  position: relative;
}
.calendar .calendar-cell .week-label {
  position: absolute;
  left: -20px;
  top: 0;
  bottom: 0;
  width: 20px;
  text-align: center;
  font-size: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #eee;
}