button{
    width: 100px;
    height: 100px;
    border-radius: 60px;
    border: none;
    background-color: hsl(0, 1%, 30%);
    color: white;
    font-size: 3rem;
    font-weight: bold;
    cursor: pointer;
}
#keys{
    display: grid;
    grid-template-columns: repeat(4,1fr);
    gap: 10px;
    padding: 30px;
}
#cal{
    font-family: 'Lucida Sans', 'Lucida Sans Regular', 'Lucida Grande', 'Lucida Sans Unicode', Geneva, Verdana, sans-serif;
    background-color: hsl(0, 3%, 15%);
    border-radius: 20px;
    max-width: 500px;
    overflow: hidden;
}
#display{
    width: 100%;
    padding: 25px;
    font-size: 5rem;
    text-align: left;
    border: none;
    background-color: hsl(0, 2%, 20%);
    color: white;
}
body{
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin-top: 100px;
    background-color: hsl(0, 10%, 90%);
}
button:hover{
    background-color: hsl(0, 1%, 47%);
}
button:active{
    background-color: hsl(0, 2%, 68%);
}
.op-btn{
    background-color: hsl(39, 88%, 52%);
}
.op-btn:hover{
    background-color: hsl(39, 61%, 47%);
    cursor: pointer;
}
@media (max-width: 600px) {
  #cal {
    max-width: 100%;
    padding: 10px;
    border-radius: 10px;
  }

  #display {
    font-size: 3rem;
    padding: 15px;
  }

  #keys {
    gap: 8px;
    padding: 15px;
  }

  button {
    width: 70px;
    height: 70px;
    font-size: 2rem;
  }
}