h1 {
    font-size: 40px;
    margin: 30px;
    margin-top: 100px;
    text-align: center;
    font-family: 'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;
}

.calculator {
    margin: 20px auto;
    width: 250px;
    height: 370px;
    background-color: #C0C0C0;
    box-shadow: 0px 0px 0px 10px #666;
    border: 5px solid black;
    border-radius: 10px;
}

#display {
    width: 320px;
    height: 40px;
    text-align: right;
    background-color: black;
    border: 3px solid white;
    font-size: 20px;
    padding-right: 5px;
    color: #7FFF00;
}

.btnTop {
    color: white;
    background-color: #6f6f6f;
    font-size: 18px;
    margin: auto;
    width: 50px;
    height: 27px;
    border-radius: 4px;
}

.btnNum {
    color: white;
    background-color: black;
    font-size: 18px;
    margin: auto;
    width: 50px;
    height: 27px;
    border-radius: 4px;
}

.btnMath {
    color: white;
    background-color: #ff4561;
    font-size: 18px;
    margin: auto;
    width: 50px;
    height: 27px;
    border-radius: 4px;
}

.btnOpps {
    color: white;
    background-color: #ff9933;
    font-size: 18px;
    margin: auto;
    width: 50px;
    height: 27px;
    border-radius: 4px;
}