Why Do Sticky Table Headers Lose Their Borders, and How Can I Fix It?

Border Style Issue with Sticky Positioned Elements

In HTML, applying position: sticky to an element can create a unique rendering issue when it comes to borders. This issue arises when the sticky element's border interacts with other elements in the layout.

The Problem:

When an element is positioned sticky, it becomes fixed after the user scrolls past a certain point. However, the borders of the sticky element may not adhere to the element if the following conditions are met:

• The parent element has border-collapse: collapse (the default value).
• The sticky element is a table header ().

The Reason:

Border collapse in CSS combines the borders of adjacent cells or elements, creating a single border. In the case of a sticky table header, the borders of the elements can be affected by this border collapse, causing them to disappear or behave unexpectedly.

The Solution:

To resolve this issue, there are two approaches:

1. Use border-collapse: separate

Changing border-collapse: collapse to border-collapse: separate ensures that the borders do not collapse. Each element (including the sticky header) will have its independent borders.

2. Style the borders explicitly

Instead of relying on CSS inheritance, explicitly apply borders to the sticky element. This can be done by using the following properties:

• border-top: Set the top border of the sticky header.
• border-bottom: Set the bottom border of the sticky header.
• border-left: Set the left border of the sticky header (for the first column only).
• border-right: Set the right border of the sticky header (for the last column only).

Example:

table {
  border-collapse: separate;
}

table th {
  border-top: 2px solid;
  border-bottom: 2px solid;
}

table th:first-child {
  border-left: 2px solid;
}

table th:last-child {
  border-right: 2px solid;
}

table thead th {
  position: sticky;
  top: 0;
  background-color: #edecec;
}

By implementing one of these solutions, you can ensure that the borders of your sticky table header remain visible and behave as intended, even when the user scrolls the page.

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