style.css

body {
    margin: 0 auto;
}
.box {
    width: 222px;
    height: 222px;
}
.box, .keys {
    display: flex;
    flex-direction: column;
    flex: 1;
}
.display {
    background-color: #FAFAFA;
    text-align: right;
    border: 1px solid #282828;
    width: 100%;

}
.equals,
.row {
    display: flex;
    flex: 1;
}
.button {
    flex: 1;
    float: center;
    background-color: #212121;
    color: #FAFAFA;
    border: 1px solid #282828;
    width: 100%;
    height: 100px;
}
.clearbutton {
    flex: 1;
    float: left;
    background-color: #212121;
    color: #FAFAFA;
    border: 1px solid #282828;
    width: 100%;
    height: 100px;
}
.button-equals {
    width: 160px;
    flex: 1;
    background-color: #212121;
    color: #FAFAFA;
    border: 1px solid #282828;
    width: 100%;
    height: 100px;
}


table{
    table-layout: fixed;
    width: 100%;
    border: none;
    border-collapse: collapse;
    padding: 0;
    margin: 0;
}

input {
    width: 100%;
}

td {
   padding:0; margin:0;
}