body {

    font-family: 'Roboto', sans-serif;

    display: flex;

    justify-content: center;

    align-items: center;

    height: 100vh;

    background-color: #f4f4f4;

    margin: 0;

}

 

.calculator {

    border-radius: 5px;

    box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.2);

}

 

.calculator-screen {

    width: 100%;

    height: 80px;

    border: none;

    background-color: #252525;

    color: #fff;

    text-align: right;

    padding: 20px;

    font-size: 2.5rem;

    border-top-left-radius: 5px;

    border-top-right-radius: 5px;

    box-sizing: border-box;

}

 

.calculator-keys {

    display: grid;

    grid-template-columns: repeat(4, 1fr);

    grid-gap: 10px;

    padding: 20px;

    background-color: #252525;

    border-bottom-left-radius: 5px;

    border-bottom-right-radius: 5px;

}

 

button {

    height: 60px;

    border-radius: 5px;

    border: none;

    font-size: 1.5rem;

    cursor: pointer;

}

 

button:active {

    box-shadow: 0 5px #666;

    transform: translateY(4px);

}

 

.operator {

    background-color: blue;

    color: white;

}

 

.equal-sign {

    background-color: blue;

    color: white;

    grid-column: span 2;

}

 

.all-clear {

    background-color: blue;

    color: white;

}

 

.decimal {

    background-color: #666;

    color: white;

}

 

button:not(.operator):not(.equal-sign):not(.all-clear):not(.decimal) {

    background-color: #e0e0e0;

    color: #252525;

}