body {
    font-family: sans-serif;
    background-color: black;
}
    
#container {
    widows: 1000px;
    height: 800px;
    background-image: url(https://images.theconversation.com/files/207820/original/file-20180226-140213-yox11e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=926&fit=clip);
    margin: 20px auto;
}

#calculator {
    width: 320px;
    height: 520px;
    background-color: #b2d5ecec;
    margin: 0 auto;
    top: 100px;
    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, 0.19);
}

#result {
    height: 120px;
}
#history {
    text-align: right;
    height: 20px;
    margin: 0 20px;
    padding-top: 20px;
    font-size: 15px;
    color: #919191;
}

#output {
    text-align: right;
    height: 60px;
    margin: 10px 20px;
    font-size: 30px;
}

#keybord {
    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 {
    background-color: #eaedef;
}

.empty {
    background-color: #b2d5ec00;
}

.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;
}