index.css

* {
    color: #eee;
    font-family: 'Courier New', Courier, monospace;
    font-size: 10vh;
    margin: 0;
    letter-spacing: 1px;
    line-height: 120%;
    word-break: break-all;
}

body {
    display: grid;
    grid-template-rows: 1fr 1fr;
    height: 100svh;
    overflow: hidden;
    background-color: #333;
}

textarea,
#highlight {
    grid-row: 1 / span 1;
    grid-column: 1 / span 1;
    margin: 5px;
    resize: none;
    background-color: transparent;
    border: 1px solid #AAA;
    border-radius: 0;
    padding: 1vh;
    overflow-y: auto;
}

#highlight {
    background-color: #444;
    white-space-collapse: preserve;
}

#highlight,
#highlight * {
    color: transparent;
    pointer-events: none;
    user-select: none;
}

#result {
    display: flex;
    justify-content: center;
    align-items: center;
    overflow-y: auto;
    border: 1px solid transparent;
    margin: 5px;
}

.highlight-content {
    background-color: #AAA;
    border-radius: 3vh;
}