style.css

body {
    width: 50%;
    min-width: 400px;
    margin: auto;
    text-align: center;
    background-color: #212121;
    font-family: "Fira Sans", sans-serif;
}
main {
    color: #FFF;
}
footer {
    font-size: 0.8em;
    color: #777;
}
h1 {
    font-size: 4em;
    margin: 0.2em;
}
h2 {
    color: #735BC1;
    font-size: 3em;
    margin: 0.2em;
}
h3 {
    font-size: 1.4em;
    margin: 0.4em;
    font-weight: 200;
}
a {
    color: #735BC1;
    text-decoration: none;
}
a:hover {
    color: #fff;
}
textarea {
    background-color: #dadada;
    resize: none;
    border: none;
    border-radius: 2px;
    font-family: "Fira Mono", monospace;
    padding: 0.3em;
    font-size: 0.8em;
    margin: 0.4em;
    opacity: 0.7;
    transition: opacity 0.2s;
}
textarea:hover {
    opacity: 1
}
p {
    margin: 0.2em;
}
#input {
    width: 100%;
}
#output {
    width: 100%;
}
button {
    font-family: "Fira Sans", sans-serif;
    font-size: 1em;
    background-color: #735BC1;
    color: #fff;
    text-transform: uppercase;
    cursor: pointer;
    margin: 0.4em;
    border: none;
    border-radius: 2px;
    padding: 4px 16px 4px 16px;
    min-width: 64px;
}