<div style="height: 400px;">
  <as-split direction="horizontal">
    <as-split-area size="40">
      <as-split direction="vertical">
        <div *asSplitGutter>
          <span asSplitGutterDragHandle class="custom-gutter">Test</span>
        </div>
        <as-split-area>
          <div class="bg"></div>
        </as-split-area>
        <as-split-area>
          <div class="bg"></div>
        </as-split-area>
      </as-split>
    </as-split-area>
    <as-split-area size="60">
      <as-split-area size="25">
        <div class="bg"></div>
      </as-split-area>
      <as-split-area size="75">
        <div class="bg"></div>
      </as-split-area>
    </as-split-area>
  </as-split>
</div>