style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: Arial, sans-serif;
}

body {
    height: 100vh;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(45deg, #5ec293, rgba(51, 144, 195, 0.267));
}

nav {
    background-color: #333;
  }
  
  nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
  }
  
  nav li {
    float: left;
  }
  
  nav li a {
    display: block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
  }
  
  nav li a:hover {
    background-color: #111;
  }
.calculator {
    border: 1px solid rgba(4, 0, 0, 0.4);
    padding: 10px;
    border-radius: 16px;
    box-shadow: 0px 5px 15px rgba(4, 0, 0, 0.4);
    background: linear-gradient(45deg, #1384a3, rgba(72, 169, 248, 0.511));
    /* height: 350px; */
}

input {
    width: 300px;
    height: 90px;

    padding: 15px;
    background: transparent;

    border: none;
    text-align: right;
    box-shadow: 0px 3px 5px rgba(35, 33, 33, 0.5);
    border-radius: 16px;
    /* user-select: none; */

    cursor: default;
    font-size: 25px;
    font-weight: 500;
    color: #000;

}

input::placeholder {
    height: 100px;

    font-size: 25px;
    font-weight: 500;
    color: white;
    text-align: right;
    color: #000;
    box-shadow: 0px 3px 15px rgba(84, 84, 84, 0.2);

}

.btn {
    text-align: center;
    cursor: pointer;
    font-size: 20px;
    font-weight: 500;
    background: transparent;
    margin-top: 10px;
    height: 70px;
    width: 70px;
    border-radius: 50%;
    border: none;
    box-shadow: 5px 5px 9px rgba(4, 0, 0, 0.4);
    transition: 0.5s;
}

.btn:hover {
    box-shadow: none;
}

.equalBtn {
    background-color: rgba(154, 65, 65,0.6);
    color: rgb(2, 16, 30);
    font-weight: 700;
}

.operator {
    font-size: 25px;
    color: rgb(9, 46, 83);
}