ui: Add dividing line between heatmap and feeds in dashboard view (#11437)

ui: Add dividing line between heatmap and feeds in dashboard view (#11437)

* ui: Add dividing line between heatmap and feeds in dashboard view

I think it's necessary to add dividing line between heatmap
and feeds in dashboard view, or the first items in feed is too
near with heatmap which is not a good view.

Signed-off-by: a1012112796 <1012112796@qq.com>
* Change the implementation method

* change style

* restart ci

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>