style.css

body {
    background-color: black;
    font-family: 'Macondo', cursive;
}

header {
    background-image: url("https://sm.ign.com/ign_br/screenshot/default/giphy-2_99ec.gif");
    display: flex;
    align-items: center;
    justify-content: center;
    color: #CBFBFB;
    margin: -8px;
    margin-bottom: 10px;
    white-space: nowrap;
    overflow: hidden;
}

.cor1 {
    color: #891AA5;
}

.cor2 {
    color: #F3F98B;
}

.main {
    background-image: url("https://i.ytimg.com/vi/41vuqCTd2-U/maxresdefault.jpg");
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    border: 1px solid green;
    border-radius: 1em;
    background-color: rgba(137, 70, 166, 0.2);
    flex-wrap: wrap;
    color: rgb(0, 223, 0);
}

.options {
    color: blue;
    margin-bottom: 30px;
}

.toEncodeDiv {
    margin: 15px;
}

.entrada {
    border-radius: 5px;
    width: 300px;
    height: 150px;
    margin-top: 10px;
}

.deslocamento {
    border-radius: 5px;
    width: 60px;
    text-align: center;
    margin-top: 10px;
}

#chaveCifraDiv {
    display: none;
}

.toDecodeDiv {
    margin-top: 30px;
}

textarea {
    background-color: black;
    color: rgb(0, 180, 0);
    border: 1px solid green;
}

input {
    background-color: black;
    color: rgb(0, 180, 0);
    border: 1px solid green;
}

button {
    background-color: #891AA5;
    border-radius: 8px;
    border: 1px green solid;
    color: #CBFBFB;
    margin: 10px;
    width: 40%;
    transition: 0.4s;
}

button:hover {
    background-color: rgb(197, 41, 236)
}

button:active {
    transform: translateY(5px);
}

footer {
    background-image: url("https://sm.ign.com/ign_br/screenshot/default/giphy-2_99ec.gif");
    display: flex;
    align-items: center;
    justify-content: center;
    color: #CBFBFB;
    margin: -8px;
    margin-top: 10px;
}

.animation {
    animation: animate 2.2s linear infinite;
}

@keyframes animate {
    0% {
        opacity: 1;
    }
    50% {
        opacity: 0.1;
    }
    100% {
        opacity: 1;
    }
}