* {
    margin: 0;
    padding: 0;
}

body {
    background: rgb(78, 77, 77);
    min-height: 100vh;
}



.calculator {
    width: 320px;
    height: 520px;
    background: rgb(240, 240, 240);
    margin: 0 auto;
    position: relative;
    top: 20px;
    border-radius: 5px;
    box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
}

.result {
    height: 120px;
}

.keyboard {
    height: 400px;
}

.history {
    text-align: right;
    height: 20px;
    margin: 0 20px;
    padding-top: 20px;
    font-size: 20px;
    color: #7c7c7c;
}

.output {
    text-align: right;
    height: 60px;
    margin: 20px 20px 0 20px;
    font-size: 40px;
    overflow: hidden;
}

.operator, .number, .empty {
    width: 50px;
    height: 50px;
    margin: 15px;
    float: left;
    border-radius: 50%;
    border: none;
    font-weight: bold;
    font-size: 15px;
}

.number, .empty {
    background: rgb(240, 240, 240);

}

.operator, .number {
    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: #20b2aa;
}

button:nth-child(8) {
    font-size: 20px;
    background: #ffa500;
}

button:nth-child(12) {
    font-size: 20px;
    background: #f08080;
}

button:nth-child(16) {
    font-size: 20px;
    background: #7d93e0;
}

button:nth-child(20) {
    font-size: 20px;
    background: #9477af;
}