Separator

<%# Separator demo markup. The first separator is decorative; the other two are
    focusable and value-bearing, dispatching change as the arrow keys adjust them.
    The consumer-owned demo.js and demo.css turn that value into pane sizes and
    the divider's appearance. %>
<div class="separator-demo">
  <p class="separator-demo__text"><%= t("components.separator.demo.intro") %></p>
  <div
    class="separator separator--horizontal"
    data-controller="stimeo--separator"
    data-stimeo--separator-orientation-value="horizontal"></div>
  <p class="separator-demo__text"><%= t("components.separator.demo.after") %></p>

  <div class="separator-demo__split">
    <%# The primary pane. Its width follows --separator-split, so the separator's
        Value reports this pane's size: ArrowRight raises the value while moving
        the vertical divider right. %>
    <div class="separator-demo__pane" id="separator-demo-primary">
      <%= t("components.separator.demo.left") %>
    </div>
    <div
      class="separator separator--vertical"
      <%# Reuse the primary pane's visible text as the separator's name. %>
      aria-labelledby="separator-demo-primary"
      aria-controls="separator-demo-primary"
      data-controller="stimeo--separator"
      data-stimeo--separator-orientation-value="vertical"
      data-stimeo--separator-focusable-value="true"
      data-stimeo--separator-min-value="20"
      data-stimeo--separator-max-value="80"
      data-stimeo--separator-step-value="5"
      data-stimeo--separator-value-value="50"
      data-action="keydown->stimeo--separator#onKeydown"></div>
    <div class="separator-demo__pane"><%= t("components.separator.demo.right") %></div>
  </div>

  <p class="separator-demo__text"><%= t("components.separator.demo.after_horizontal") %></p>

  <%# A horizontal separator takes ArrowUp and ArrowDown. demo.js maps the same
      --separator-split custom property onto the top / bottom pane ratio. %>
  <div class="separator-demo__split separator-demo__split--stacked">
    <div class="separator-demo__pane"><%= t("components.separator.demo.top") %></div>
    <div
      class="separator separator--horizontal-handle"
      aria-labelledby="separator-demo-primary-stacked"
      aria-controls="separator-demo-primary-stacked"
      data-controller="stimeo--separator"
      data-stimeo--separator-orientation-value="horizontal"
      data-stimeo--separator-focusable-value="true"
      data-stimeo--separator-min-value="20"
      data-stimeo--separator-max-value="80"
      data-stimeo--separator-step-value="5"
      data-stimeo--separator-value-value="50"
      data-action="keydown->stimeo--separator#onKeydown"></div>
    <%# Here the lower pane is the primary one. Flexing the last child from
        --separator-split makes ArrowUp raise the primary pane's value while
        moving the divider up. %>
    <div class="separator-demo__pane" id="separator-demo-primary-stacked">
      <%= t("components.separator.demo.bottom") %>
    </div>
  </div>
</div>

/*
 * Presentation-only styles for the separator demo.
 * The line's rendering, color, and thickness are owned by the consumer's CSS. The
 * library only gives meaning to role / aria-orientation / aria-valuenow.
 */

.separator-demo {
  max-width: 32rem;
}

.separator-demo__text {
  margin: 0.5rem 0;
}

.separator--horizontal {
  height: 1px;
  margin: 0.75rem 0;
  background: var(--border-strong);
}

.separator-demo__split {
  display: flex;
  align-items: stretch;
  height: 6rem;
  margin-top: 1rem;
  border: 1px solid var(--border-default);
  border-radius: 0.5rem;
  overflow: hidden;
  /* demo.js updates this variable from aria-valuenow (%) to set the left pane's width. */
  --separator-split: 50%;
}

.separator-demo__pane {
  display: grid;
  place-items: center;
  padding: 0.5rem;
  background: var(--surface-subtle);
}

.separator-demo__pane:first-child {
  flex: 0 0 var(--separator-split);
}

.separator-demo__pane:last-child {
  flex: 1;
}

.separator--vertical {
  flex: 0 0 0.5rem;
  background: var(--border-strong);
  cursor: col-resize;
}

/* Use :focus (not :focus-visible) so the color inversion shows on click too, not
   only on keyboard focus — a resize handle is dragged with the mouse, and the user
   needs to see it took focus. (Same reasoning as the time_picker demo.) */
.separator--vertical:focus {
  outline: 2px solid var(--accent);
  outline-offset: -2px;
  background: var(--accent);
}

/* Horizontal, value-bearing separator: a top/bottom split. Stacks the panes vertically;
   the value-to-pane mapping (the bottom pane) is handled by the rules just below. */
.separator-demo__split--stacked {
  flex-direction: column;
  height: 9rem;
}

/* Size the BOTTOM pane from the value so ArrowUp (increase) moves the handle up (the top
   shrinks) — the handle follows the arrow direction instead of moving the opposite way. */
.separator-demo__split--stacked .separator-demo__pane:first-child {
  flex: 1;
}

.separator-demo__split--stacked .separator-demo__pane:last-child {
  flex: 0 0 var(--separator-split);
}

.separator--horizontal-handle {
  flex: 0 0 0.5rem;
  background: var(--border-strong);
  cursor: row-resize;
}

.separator--horizontal-handle:focus {
  outline: 2px solid var(--accent);
  outline-offset: -2px;
  background: var(--accent);
}

// Consumer-side JS for the separator demo (optional).
// A valued, focusable separator increments/decrements aria-valuenow with the arrow
// keys and fires stimeo--separator:change with { value }.
// Here we reflect that value (%) into the left pane's width to visualize the resize.
// The actual layout/size computation is the consumer's job (the library only gives the
// value meaning).
document.addEventListener("stimeo--separator:change", (event) => {
  const split = event.target.closest(".separator-demo__split");
  if (!split) return;
  split.style.setProperty("--separator-split", `${event.detail.value}%`);
});