index.css

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: transparent;
    margin: 0;
    font-family: Arial, sans-serif;
    background-image: ;
}

.calculator {
    border: 10px solid #230909;
    padding: 18px;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 0 20px rgba(0,0,0,0.1);
    background-color: #030303;
}

#display {
    width: 83%;
    height: 60px;
    font-size: 2em;
    text-align: right;
    
    padding: 20px ;
    border: none;
   
    outline: none;
    background-color: #00ccff;
    color: white;
    margin-left: 15px;
    margin-bottom: 5px;
    
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    border: 5px transparent;
    padding: 15px;
    
}

.btn {
    width: 100%;
    padding: 20px;
    border: 3px transparent;
    border-radius: 10px;
    background-color: rgb(109, 106, 106);
    font-size: 1.5em;
    cursor: pointer;
}

.btn:active {
    background-color: #211a16;
    
}
.btn:hover {
    color: #00ccff;
}