I created a minimal example (directly editable online). I have two questions on how to tweak it to look better.
First of all, how to set the height to 100%? The problem is the the "category" selectize which goes "inside" of the outer box.
How to get rid of these borders around the outer box. What helped on one page was ui.tags.style(ui.HTML(".bslib-sidebar-layout .sidebar { border: 0px; }")),
I'd say it's a very straight forward once you know the targeted CSS class name, you could use Global Styling.
Here's an example where I apply global styling to the ui.page_fluid
shiny component, where everything is placed in the shiny app: