main.css

body {
    padding: 0;
    margin: 0;
}

.container {
    position: relative;
    padding: 0;
    height: 100vh;
    width: 100vw;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: rgba(155, 197, 195, 1);
    background: -moz-linear-gradient(-45deg, rgba(155, 197, 195, 1) 0%, rgba(97, 97, 97, 1) 100%);
    background: -webkit-gradient(left top, right bottom, color-stop(0%, rgba(155, 197, 195, 1)), color-stop(100%, rgba(97, 97, 97, 1)));
    background: -webkit-linear-gradient(-45deg, rgba(155, 197, 195, 1) 0%, rgba(97, 97, 97, 1) 100%);
    background: -o-linear-gradient(-45deg, rgba(155, 197, 195, 1) 0%, rgba(97, 97, 97, 1) 100%);
    background: -ms-linear-gradient(-45deg, rgba(155, 197, 195, 1) 0%, rgba(97, 97, 97, 1) 100%);
    background: linear-gradient(135deg, rgba(155, 197, 195, 1) 0%, rgba(97, 97, 97, 1) 100%);
    filter: progid: DXImageTransform.Microsoft.gradient( startColorstr='#9bc5c3', endColorstr='#616161', GradientType=1);
}

.credits a,
p {
    font-size: 10px;
    color: #fff;
}

#result p {
    font-size: 18px;
    color: #fff;
    font-weight: 600;
}

.input {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 100%;
}

.input input {
    width: 80%;
    background-color: white;
    padding: 20px;
    text-align: right;
    font-size: 18px;
}

.input button {
    display: block;
    width: 20%;
    padding: 10px;
    background-color: #50C9C3;
    color: #fff;
    border: none;
    font-size: 18px;
    margin: 15px auto;
    cursor: pointer;
    -webkit-box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.35);
    -moz-box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.35);
    box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.35);
}