Why Doesn't My CSS `text-decoration` Work as Expected on Nested Elements?

Dealing with CSS Text Decoration Quirks

In CSS, the text-decoration property plays a crucial role in styling text elements. However, applying text-decoration may not always behave as expected. This article delves into the complexities of CSS text decoration and provides a solution to a common issue.

The Problem

A developer encountered a puzzling situation where inline CSS rules for text-decoration seemed to have no effect on nested elements. They had written the following code:

ul > li {
    text-decoration: none;
}
ul > li.u {
    text-decoration: underline;
}
ul > li > ul > li {
    text-decoration: none;
}
ul > li > ul > li.u {
    text-decoration: underline;
}

This CSS was expected to underline only the li elements with the class "u" and leave all other li elements with no decoration. However, in practice, all li elements were being underlined.

The Solution

The issue lies in the unique behavior of text-decoration. Unlike other text styling properties like font-weight, text-decoration affects not only the element it's applied to but also its descendant elements.

As per the CSS 2.1 specification, text decoration is drawn across the entire element, regardless of any descendant elements. This means that setting text-decoration on a parent element will propagate the decoration to its children, even if they have their own text-decoration rules.

In the example provided, the text-decoration: none; rule on the second and third selectors was not effective because the decoration was already being propagated from the first selector.

Conclusion

Understanding this quirk in CSS text decoration is essential for preventing unexpected results. By applying text-decoration only to the outermost elements and relying on inheritance for nested elements, developers can ensure that their CSS text decoration rules behave as intended.

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