Attempting to mimic the Slack layout has been a challenge. The one hurdle I can't seem to overcome is overlapping the date over the header. After inspecting Slack's HTML/CSS, it seems they use a mix of Sticky and absolute positioning. My preference, however, would be to utilize relative positioning.
HTML
<html>
<head>
<title>Slack</title>
<link href="https://a.slack-edge.com/bv1-8-8cacda2/slack-icons-v2-71d3b78.woff2" rel="preload" as="font" crossorigin="anonymous">
<link href="https://a.slack-edge.com/bv1-8-8cacda2/lato-regular-d9ce515.woff2" rel="preload" as="font" crossorigin="anonymous">
... (and so on)
</body>
</html>
CSS
/************ reset ************/
...
/************ fonts ************/
...
@font-face {
font-family: Slack-Lato;
font-style: normal;
font-weight: 300;
src: local("\263A"), url(https://a.slack-edge.com/bv1-8-8cacda2/lato-light-0b50f74.woff2) format("woff2"), ...;
unicode-range: U+0000-f8fe, U+f900-ffff
}
... (remaining font definitions)
/********************************/
.p-client {
overflow: hidden;
}
...
/**********************/
Sticky under header: