I saw that it took a million times. In general, what I will do is:
Fiddle
Basically insert an inner container inside it with the background color of the side panel and set the side panel to transparent. Then, if you want the background to appear in the gutter, place the border on the right in the main content area so that you get a kind of artificial gutter.
Warning. The main content area should be longer than the sidebar, or the "gutter" will be displayed as far as the main content area. I usually fix this by setting a minimum height in the main content area.
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