html,
body {
    font-style: sans-serif;
    font-family: 'Montserrat', sans-serif;
}

.h1 {
    width: 100%;
    text-align: center;
}

.bg-white {
    background-color: #fff;
}

.bg-gray {
    background-color: #ebebeb;
}

.bg-yellow {
    background-color: #ffd90b;
}

.bg-red {
    background-color: #ff9b9b;
}

.calculator {
    max-width: 25em;
    margin: auto;
}

.input-box {
    text-align: right;
    padding: 12px;
    border: 1px solid rgba(0, 0, 0, .3);
    border-bottom: none;
}

.section {
    height: 250px;
    border-bottom: 1px solid rgba(0, 0, 0, .3);
    border-right: 1px solid rgba(0, 0, 0, .3);
    display: flex;
    flex-wrap: wrap;
}

.cell {
    padding: 0;
    margin: 0;
    border: none;
    height: 50px;
    text-align: center;
    font-size: 1.6em;
    transition: 100ms;
    border-left: 1px solid #c8c8c8;
    border-top: 1px solid #c8c8c8;
    border-radius: 0;
}

.cell:hover {
    filter: brightness(90%);
    cursor: pointer;
}

.single {
    width: 25%;
}

.double {
    width: 50%;
}

.triple {
    width: 75%;
}

.error {
    background-color: rgba(255, 176, 145, 0.712);
    color: rgb(105, 30, 0);
}