Why Is There a Vertical Scrollbar Even When Parent and Child Heights Seem Equal?

Identifying the Unexpected Vertical Scroll Bar

When designing a web layout, you may encounter situations where the parent and child elements seemingly have equal heights, yet a vertical scroll bar still appears. This is a common issue that can be attributed to CSS configurations.

The Role of Vertical-Align Property

The crux of the issue often lies in the default vertical-align property for inline-level elements, which is "baseline." In typography, this refers to the line on which most letters rest, while some letters extend below it (descenders). By default, inline-level elements like buttons, inputs, and inline-block divs are aligned at the baseline, which creates extra space below them for descenders.

In the given code example, where .displayContainer houses .sideBar and .contentHolder as inline-block elements, this extra descender space adds to the container's height. When the available height is exceeded, an overflow occurs, triggering the appearance of a vertical scroll bar.

Eliminating the Vertical Scroll Bar

To resolve this issue and remove the unnecessary vertical scroll bar, you can implement various approaches:

• Override Vertical-Align: Change the vertical-align property to "top," "bottom," or "middle" to rectify the issue.
• Use Display: Block: Instead of using display: inline-block, switch to display: block.
• Set Parent's Line-Height: Assign line-height: 0 to the parent container to eliminate vertical spacing.
• Set Parent's Font-Size: Set font-size: 0 to the parent, but consider restoring it on the child elements if needed.

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