Section#chat-window styles don't work

Hello, does anyone know why this could possibly not work?

section#chat-window-tV3BGE3xZncEx7Lmb .title, .read-receipt, .start {
    display: none;
}

When I type that in developer tools, it works and hides the specified elements on the page but when I put this in Layout>Custom CSS and reload the page it doesn’t work.