/* ====================================================================
   SHELL · root layout grid
   ====================================================================
   Desktop-first. 320 / 1fr / 320 columns. Top bar spans all three.
   Sidebars start under the top bar.
   ==================================================================== */

.io-shell {
  display: grid;
  grid-template-columns: 320px 1fr 320px;
  grid-template-rows: 60px 1fr;
  grid-template-areas:
    "left  top   top"
    "left  main  right";
  height: 100vh;
  width: 100vw;
  background: var(--io-surface-base);
}

.io-shell__top {
  grid-area: top;
  background: var(--io-surface-sunken);
  border-bottom: 1px solid var(--io-border);
  position: relative;
  z-index: 2;
}

.io-shell__left {
  grid-area: left;
  background: var(--io-surface-sunken);
  border-right: 1px solid var(--io-border);
  overflow-y: auto;
  overflow-x: hidden;
}

.io-shell__right {
  grid-area: right;
  background: var(--io-surface-sunken);
  border-left: 1px solid var(--io-border);
  overflow-y: auto;
  overflow-x: hidden;
}

.io-shell__main {
  grid-area: main;
  background: var(--io-surface-base);
  overflow-y: auto;
  overflow-x: hidden;
  position: relative;
}