style.css

@import url("https://fonts.googleapis.com/css2?family=Poppins:wght@400;500&display=swap");
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: "Poppins", sans-serif;
}

.flex {
    display: flex;
    align-items: center;
    justify-content: center;
}

.container {
    width: 100%;
    height: 100vh;
    background-color: rgb(33, 32, 32);
}


/* @CoderMo */

.calendar {
    width: 430px;
    height: 500px;
    background-color: white;
    box-shadow: 10px 10px 20px rgba(0, 0, 0, 0.669), -10px -10px 20px rgba(0, 0, 0, 0.436);
}

.calendar .month {
    width: 100%;
    height: 20%;
    padding: 20px 30px;
    background-color: #0093e9;
    background-image: linear-gradient( 90deg, #0093e9 0%, #037cc2 55%, #59c1fd 100%);
    justify-content: space-between !important;
    text-align: center;
}

.calendar .month img {
    width: 26px;
    height: 26px;
    cursor: pointer;
    transition: 0.1s;
}

.month img:hover {
    opacity: 0.8;
}

.month h1 {
    text-transform: uppercase;
    font-size: 30px;
    color: #fff
}

.month p {
    font-weight: 300;
    color: #fff;
    font-family: cursive;
}


/* @CoderMo */

.weekdays {
    width: 100%;
    padding: 10px;
    height: 10%;
    padding-bottom: 0;
}

.weekdays div {
    width: calc(430px / 7);
    height: 80%;
    text-align: center;
    font-size: 16px;
    font-weight: 500;
    margin: 0 5px;
    transition: 0.2s;
}

.days {
    width: 100%;
    height: 70%;
    flex-wrap: wrap;
    margin: auto;
    padding: 30px 10px;
    padding-top: 0;
}

.days div {
    width: calc(400px / 7);
    height: calc(400px / 7);
    text-align: center;
    font-size: 13.5px;
    font-family: cursive;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: 0.1s;
}

.days .previous-days,
.days .next-days {
    color: #fff;
}

.days .today {
    background-color: #0093e9;
    cursor: pointer;
    color: white;
    border-radius: 50%;
    transition: 0.2s;
}

.days .today:hover {
    background-color: #0093e9;
}

.days div:not(.today):hover {
    border-radius: 0;
    border: 0.5px solid white;
    background-color: rgba(0, 0, 0, 0.215);
    cursor: pointer;
}