CSS How to Set an Outline Border on a colgroup

In this article, we’ll explain how to set an outline border on the colgroup element. The colgroup element is used to define a group of columns in a table. It contains one or more col elements and sets common properties for them.

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1. Using the border-collapse Property

To set an outline border on a colgroup, we can use the border-collapse property. This property specifies the border model of a table and has two possible values: collapse and separate. We need to set it to collapse.

table { border-collapse: collapse; 
}

The above code example will collapse the table’s borders, allowing the colgroup’s outline border to show through. Note that this property must be applied to the entire table, not just the colgroup element.

2. Using the outline property

In addition to using the border-collapse property, we can also use the outline property to create an outline border. The outline property adds a visible outline to an element without changing its size or position.

colgroup {
outline: 1px solid black;
}

The above code example will create a 1px black border around the colgroup element. We can adjust the border’s width, color, and style as needed.

3. Using Pseudo-Elements

If we want the outline border of a colgroup element to have other special effects, we can use pseudo-elements to achieve this. Here’s an example code:

colgroup::before {
content: "";
position: absolute;
top: -2px;
left: -2px;
right: -2px;
bottom: -2px;
border: 2px dashed red;
}

The above example code will create a 2px thick red dashed border around the colgroup element. We can adjust the border’s width, style, and color to achieve different effects as needed.

Summary

This article introduced how to set an outline border on a colgroup element. We can use the border-collapse property to merge the table’s borders into a single entity, making the colgroup’s outline visible. We can also use the outline property to add a visible outline border to the colgroup element, or use pseudo-elements to achieve other special effects. Choosing the appropriate method to set outline borders based on actual needs can make the table’s style richer and more flexible.