body{
    background-color: black;
}
body #container{
    background-color: #eaedef;
    width: 350px;
    height: 600px;
    position: relative;
    margin: 2em auto;
    text-align: center;
    border-radius: 5px;
}
header{
    padding: 10px;
    font-size: 2em;
}
#calculator{
    padding: 10px;
}
#result{
    margin: 1em auto;
    padding: 10px;
    text-align: right;
    height: 100px;
}
#history{
    font-size: 1.2em;
    padding: 15px;
}
#output{
    font-size: 1.5em;
    padding: 15px;
    font-weight: bolder;
}
#keyboard{
    padding: 15px;
    margin: 1em auto;
    width: 280px;
}
button{
    width: 60px;
    height: 60px;
    padding: 2px;
    margin: 2px;
    border-radius: 25%;
    border: 0;
    font-weight: bold;
    font-size: 20px;
}
.number, .empty{
	background-color: #eaedef;
}
.number, .operator{
	cursor: pointer;
}
.operator:active, .number:active{
	font-size: 13px;
}
.operator:focus, .number: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;
}