How do `font-size`, `line-height`, and `actual height` interact to influence element dimensions?

Understanding the Roles of font-size, line-height, and Actual Height

Determining the heights of elements can be confusing when dealing with seemingly contradictory attributes like font-size and line-height. This article aims to clarify the interplay between these properties and their impact on the actual height of elements.

Font-size vs Line-height

Font-size determines the height of the box enclosing letters (including ascenders and descenders). Line-height, on the other hand, specifies the height of the "line box," which includes the font-size and additional space for spacing between lines.

Actual Height: A Complex Calculation

The actual height of an element is influenced by multiple factors:

• For inline elements: The line-height of the element.
• For div elements that contain inline elements: The line-height of the div and the height of the line box established by the inline elements within it.

Effects of Line-height on Actual Height

• When line-height is less than font-size: The line box is smaller than the line-height specified for the element, resulting in a smaller actual height for the div.
• When line-height is greater than font-size: The line box expands beyond the height of the font-size, increasing the div's actual height.

Additional Considerations

• Strut: In some cases, an invisible "strut" is added to the top and bottom of the line box based on the line-height of the parent block. This can affect the actual height of the element.
• Vertical-align: The vertical-align property can adjust the position of the text vertically within the line box, impacting the actual height under certain conditions.

Conclusion

Understanding the combined effects of font-size, line-height, and actual height is crucial in achieving desired spacing and precise element positioning. By grasping the intricacies of these properties, you can ensure accurate height calculations and consistent rendering across different browsers.

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