How can I create a custom box-shadow that shades all sides of an element except for one?

Applying Box-Shadow to Specific Sides of an Element

In this CSS3-related question, the user seeks to create a custom box-shadow that, unlike a traditional box-shadow, would shade all sides of an element except for one. The desired outcome is to have a tabbed navigation bar with a visible shadow on the open tab and a separate shadow at the bottom of the entire tab section.

The key to tackling this problem lies in understanding the parameters of the box-shadow property. CSS3's box-shadow takes four separate values:

1. Horizontal offset: Distance of the shadow to the left or right
2. Vertical offset: Distance of the shadow above or below
3. Blur radius: Amount of blur applied to the shadow
4. Spread: Offset added to the size of the shadow box

In this specific scenario, we can control the shading of only certain sides by manipulating these values.

To create the top and inward-facing side shadow for the entire tab section, we set the first two values to 0 (zero offset) and adjust the blur radius and spread accordingly.

For the individual tab's shadow, we create a div within the #content element and position it relative to the parent. The new div receives a solid background and has its shadow defined. The parent #content itself has its paddings removed and a separate shadow added.

Finally, to apply the shadows to each tab, we target the anchors within the #nav li elements. We position them relative to their parent and define the desired shadow values.

By employing these techniques, the user can achieve the desired shading effect on all sides of the tab element except for the open one, effectively setting it apart from the other tabs.

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