:root {
    --color-link: hsl(220, 80%, 50%);
    --color-error: hsl(350, 100%, 45%);
    --color-bg-article: hsl(110, 100%, 95%);
    --color-border-1: hsla(0, 0%, 0%, 13%);
    --color-border-2: hsla(0, 0%, 0%, 20%);
    --color-fg: hsl(0, 0%, 0%);
    --color-bg: hsl(0, 0%, 100%);
}

@media (prefers-color-scheme: dark) {
    :root {
        --color-link: hsl(215, 100%, 60%);
        --color-error: hsl(350, 90%, 60%);
        --color-bg-article: hsl(140, 30%, 20%);
        --color-border-1: hsla(0, 0%, 100%, 20%);
        --color-border-2: hsla(0, 0%, 100%, 30%);
        --color-fg: hsl(0, 0%, 90%);
        --color-bg: hsl(220, 20%, 8%);
    }
}

body {
    background-color: var(--color-bg);
    color: var(--color-fg);
    display: flex;
    margin: 0;
    justify-content: center;
}

.container {
    font-family: sans-serif;
    font-size: 1.1em;
    line-height: 150%;
    margin: 1em;
    width: 100%;
    max-width: 700px;
}

.container h2 {
    font-size: 1.2em;
}

h1, h2 {
    line-height: 125%;
}

.section {
    border-top: 1px solid var(--color-border-1);
}

article {
    padding: 1em;
    background-color: var(--color-bg-article);
}

.challenge-uri-box {
    border: 1px solid var(--color-border-1);
    padding: 0.3em 0.65em;
    border-radius: 0.5em;
    width: fit-content;
    margin-bottom: 1em;
}

a, a:visited {
    text-decoration: none;
    color: var(--color-link);
}

a:hover {
    text-decoration: underline;
}

.error {
    color: var(--color-error);
}

textarea {
    width: 100%;
    height: 15em;
    background-color: var(--color-bg);
    color: var(--color-fg);
}

table {
    border-collapse: collapse;
    width: 100%;
    margin: 1em 0;
}

thead th {
    background-color: var(--color-fg);
    color: var(--color-bg);
    border-bottom: 1px solid var(--color-border-2);
    padding-top: 0.4em;
}

thead.light-header th {
    background-color: inherit;
    color: inherit;
}

tr {
    border-bottom: 1px solid var(--color-border-2);
}

td, th {
    padding: 0.3em 0.6em;
}

th {
    text-align: left;
}

.footer {
    margin: 1em 0;
    border-top: 1px solid var(--color-border-2);
    font-size: 0.65em;
    opacity: 70%;
}

header {
    border-bottom: 1px solid var(--color-border-1);
    display: flex;
    justify-content: space-between;
}

.small {
    font-size: 70%;
}