cal.css

* {
    margin:0px;
    padding: 0px;
    box-sizing: border-box;
    font-family: verdana;

}

.container {
    width:100%;
    min-height: 100vh;
    background: linear-gradient(135deg, #4203a9, #90bafc);
    color:white;
    padding:10px;
}

.calculator {
    width:550px;
    min-width: 600px;
    margin-left: 10%;
    margin-top: 10%;

}

.calculator h1 {
    font-size: 60px;
    text-shadow: 2px 2px 3px black;
    font-weight: bold;
}

.calculator h1 span {
    color:yellow;
}

.input-box {
    margin:40px 0;
    padding:35px;
    border-radius: 10px;
    background: rgba(255,255,255,0.3);
    display:flex;
    align-items: center;

}

.input-box input {
    flex:1;
    margin-right: 20px;
    padding:14px 20px;
    border:0;
    outline: 0;
    font-size: 18px;
    border-radius:5px;
    position: relative;
}

.input-box button {
    background: #f8f84a;
    border:0;
    outline:0;
    padding:15px 30px;
    border-radius: 5px;
    font-weight: 500;
    color:#333;
    cursor: pointer;
}

.input-box input::-webkit-calendar-picker-indicator {
    top:0;
    left:0;
    right:0;
    bottom:0;
    width:auto;
    position:absolute;
    background-position: calc(100% - 10px);
    background-size: 30px;
    cursor:pointer;
    height:auto;
}