body{
    font-family: 'open-sans', sans-serif;
    background-color: lemonchiffon;
}
#container{
    max-width: 1000px;
    min-height: 560px;
    background-image: url(images/planet-1702788.jpg);
    background-repeat: no-repeat;
    margin: 25px auto;
}
#calculator{
    width: 320px;
    min-height: 520px;
    background-color: #eaedef;
    margin: 0 auto;
    top: 20px;
    position: relative;
    border-radius: 5px;
    box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2), 0 6px 20px 0 rgba(0,0,0,0.2);
}
#result{
    max-height: 120px;
}
#watch{
    position: absolute;
    right: 15px;
    margin: 5px;
}
#history{
    text-align: right;
    height: 20px;
    margin: 0 20px;
    padding-top: 20px;
    font-size: 20px;
    color: darkgrey;
}
#output{
    text-align: right;
    height: 55px;
    margin: 10px 20px;
    font-size: 35px;
}
#keyboard{
    height: 400px;
}
.operator, .number, .empty{
    width: 50px;
    height: 50px;
    margin: 15px;
    float: left;
    border-radius: 50%;
    border-width: 0;
    font-weight: bold;
    font-size: 15px;
}
.number, .empty{
    background-color: #eaedef;
}
.operator{
    background-color: darkgrey;
}
.number, .operator{
    cursor: pointer;
}
.number:active, .operator:active{
    font-size: 13px;
}
.number:focus, .operator:focus, .empty:focus{
    outline: 0;
}
button:nth-child(4){
    font-size: 20px;
    background-color: #20b2aa;
}
button:nth-child(8){
    font-size: 20px;
    background-color: #ffa500;
}
button:nth-child(12){
    font-size: 20px;
    background-color: #f08080;
}
button:nth-child(16){
    font-size: 20px;
    background-color: #7d93e0;
}
button:nth-child(20){
    font-size: 20px;
    background-color: #9477af;
}