style.css

body{
    font-family: 'Sarasa Mono SC';
    background-color: #2e3440;
    text-align: center;
}
#calculator{
    width: 320px;
    height: 520px;
    background-color:#3b4252;
    margin: auto;
    top: 50px;
    position: relative;
    border-radius: 20px;
    box-shadow: 4px 4px 8px rgba(0, 0, 0, 0.5);
}
#result{
    height: 120px;
}
#keyboard{
    height: 400px;
}
#history{
    text-align: right;
    height: 20px;
    margin: 10px 20px;
    padding-top: 20px;
    font-size: 15px;
    color: #d8dee9;
}
#output{
    text-align: right;
    height: 60px;
    margin: 0 20px;
    font-size: 30px;
    color: #eceff4;
}
.operator, .number, .functionKeys,.decorator{
    width: 50px;
    height: 50px;
    margin: 15px;
    float: left;
    border-radius: 30%;
    font-family: "Sarasa Mono SC";
    color: #2e3440;
    border-width: 0;
    font-weight: bold;
    font-size: 18px;
}
.number, .operator,.functionKeys,.decorator{
    cursor: pointer;
}
.operator:active, .number:active, .functionKeys:active,.decorator:active{
    font-size: 15px;
}
.operator:focus, .number:focus{
    outline: 0;
}
.operator{
    background-color: #ebcb8b;
}
#equal{
    background-color: #bf616a;
}
.functionKeys{
    background-color: #a3be8c;
}
.number{
    background-color: #88c0d0;
}
.decorator{
    background-color: #d08770;
}

#foot{
    color:#78849b;
    font-size: 14px;
    position:fixed;
    bottom: 10px;
    width: 100%;
    text-align: center;
}