pico.chat/pico.css

body {
    margin: 0;
    padding: 0;
}
.chat {
    display: grid;
    grid-template-areas:
        'posts users'
        'actions users'
    ;
    grid-template-columns: 1fr auto;
    grid-template-rows: 1fr auto auto;

    height: 150px;
    position: fixed;
    top: 0;

    --pad: 3px;
    padding: var(--pad);
    width: calc(100vw - 2 * var(--pad));
}
.ts {
    color: rgba(0, 0, 0, 0.4);
    font-family: monospace;
}
.source {
    font-weight: bold;
}
.users {
    grid-area: users;
}
.posts {
    grid-area: posts;
    overflow-y: scroll;
}
.actions {
    grid-area: actions;
}
.post > div {
    display: inline;
    padding-left: var(--pad);
}