How to Extend a Flexbox Aside's Background Color to Overflowing Content Dynamically?

Make Background Color Extend into Overflow Area

Issue

In a Flexbox layout, the aside element's background color doesn't extend the full height of the parent container, even though the content height is significantly greater than the visible area. How do we make the background color stretch dynamically to the bottom of the content?

Limitations

• No additional elements can be added.
• The aside element must scroll with the parent content.
• The background color must extend from the top to the bottom of the container.
• The aside element cannot have its own overflow: auto.
• The solution must be dynamic and not rely on a fixed height.

Analysis

Part I: Background Color

CSS background properties extend up to the element's borders, not including the margin area. In this case, the overflow area is outside the #body element's borders, resulting in a truncated background color.

Part II: Overflow

The overflow property only controls the display of content, not backgrounds. The overflowing content is clipped, not the background.

Solution

This problem cannot be solved solely with CSS due to the limitations mentioned above. A JavaScript solution is required.

JavaScript can dynamically adjust the #body element's height to match the content size. This ensures that the background color extends to the bottom of the container.

Here's an example code snippet:

document.getElementById("body").style.height = document.documentElement.scrollHeight + "px";

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