As I was trying to separate normal threads from sticky ones I finally managed to do it and it was very simple. There is no need for template modification whatsoever.
1- Go to template forum_view
2- find this code
Code:
<xf:macro template="thread_list_macros" name="item" arg-thread="{$thread}" arg-forum="{$forum}" />
</xf:foreach>
</div>
3- Place this code below the above code and hit save.
Code:
<xf:if is="{$stickyThreads}">
<hr class="stickySeparator"/>
</xf:if>
4- Now go to template extra.less and add this
You can play with the css code in case you want to change the color or the hight of the bar as I did below in the screenshot.
Here is the after math.

1- Go to template forum_view
2- find this code
Code:
<xf:macro template="thread_list_macros" name="item" arg-thread="{$thread}" arg-forum="{$forum}" />
</xf:foreach>
</div>
3- Place this code below the above code and hit save.
Code:
<xf:if is="{$stickyThreads}">
<hr class="stickySeparator"/>
</xf:if>
4- Now go to template extra.less and add this
Hit save and you are good to go.
You can play with the css code in case you want to change the color or the hight of the bar as I did below in the screenshot.
Here is the after math.