Starting with this Demo Template, I would like to create this layout:

But I have the following problems:
- The two sidebars are not contained inside the scrollable content div.
- The content div does not take a fixed size
- The scrollable content does not present a scrollbar when it overflows
- It is preferred if the browser’s main scrollbar is used
Can someone help me to fix these issues?
Using
display:gridThis uses several new features of CSS that may or may not be supported in your browser of choice. These include Grid Layout, CSS Variables, and
position:sticky. CSS Variables can be worked around with static values and Grid/position:stickycan degrade gracefully with@supports.Scrollbar in main content container
The content box (including the sidebars) can be set to any type of width (percent, pixel, etc). Only the scrollable content area will scroll (sidebars/footer/header will just overflow the box). I’d suggest adding some media queries to break out of the sidebars so content isn’t hidden on smaller devices, or set a
min-heighton the content box and amin-widthon thebody.Using the browser’s main scrollbar
While using the browser’s main scrollbar is possible, it also causes the sidebars to scroll with the page.