calendar.css

* {
    margin: 0;
    padding: 0;
}

.calendar-wrapper {
    max-width: 310px;
}

.calendar-header {
    position: relative;
    background-color: #c61b01;
    padding: 10px 0;
    overflow: auto;
}

.calendar-mid {
    position: absolute;
    left: 50%;
    -webkit-transform: translate(-50%);
    transform: translate(-50%);
}

.calendar-header .leftArrow {
    width: 0;
    height: 0;
    border-width: 10px;
    border-style: solid;
    border-top-color: transparent;
    border-bottom-color: transparent;
    border-left-color: transparent;
    border-right-color: #ffffff;
    margin-left: 5px;
    float: left;
    cursor: pointer;
}

.calendar-header .rightArrow {
    width: 0;
    height: 0;
    border-width: 10px;
    border-style: solid;
    border-top-color: transparent;
    border-bottom-color: transparent;
    border-left-color: #fff;
    border-right-color: transparent;
    margin-left: 5px;
    float: right;
    cursor: pointer;
}

ul.weekTip, ul.date {
    font-size: 0;
}

ul.weekTip > li, ul.date > li {
    display: inline-block;
    box-sizing: border-box;
    font-size: 15px;
    color: #000000;
    width: 40px;
    height: 40px;
    border-radius:50%;
    line-height: 40px;
    text-align: center;
    cursor: pointer;
    margin-bottom: 5px;
}

ul.weekTip > li:not(:nth-of-type(7n)), ul.date > li:not(:nth-of-type(7n)) {
    margin-right: 5px;
}

ul.date > li.active {
    background-color: rgb(200, 17, 1);
    color: #ffffff;
}

ul.date > li.across {
    border: 1px solid rgb(200, 17, 1);
    color: rgb(200, 17, 1);
}

ul > li.weekend {
    color: rgb(200, 17, 1);
}

ul > li.disabled {
    color: lightgray;
}

#demo {
    position: relative;}