page.module.css

.layout {
  display: grid;
  /*
    Reserve the desktop drawer's width (its default 320px) as a fixed first
    column so the layout doesn't shift when the client-only <CopilotThreadsDrawer>
    mounts after hydration. On mobile the drawer is an off-canvas overlay (out
    of flow), so the column collapses and the content fills the width.
  */
  grid-template-columns: var(--cpk-drawer-reserved-width, 320px) minmax(0, 1fr);
  /* Drawer sets --cpk-drawer-reserved-width to 0 on desktop-collapse, so the
     reserved column collapses and the chat reclaims the space. */
  transition: grid-template-columns 0.2s ease;
  /*
    Bound the single grid row to the viewport (minmax(0,1fr) lets it shrink
    below content) so a long thread list scrolls INTERNALLY in the drawer with
    the header pinned, instead of the drawer growing past the viewport and the
    page scrolling the header away.
  */
  grid-template-rows: minmax(0, 1fr);
  height: 100dvh;
  width: 100%;
  overflow: hidden;
}

.mainPanel {
  /*
    Pin the content to the SECOND track explicitly. The client-only drawer
    renders nothing during SSR, so without this the content would flow into the
    reserved first column at first paint and then jump once the drawer mounts.
  */
  grid-column: 2;
  min-width: 0;
  height: 100dvh;
  overflow: hidden;
}

/*
  Mobile (≤768px): the drawer is an off-canvas overlay — collapse to a single
  track. MUST come after the base rules (media queries add no specificity, so a
  later same-specificity base rule would otherwise win and leak the two-column
  desktop layout onto mobile).
*/
@media (max-width: 768px) {
  .layout {
    grid-template-columns: minmax(0, 1fr);
  }
  .mainPanel {
    grid-column: auto;
  }
}