How Does Content-Box Height Differ for Block and Inline Elements?

Determining the Height of Content-Boxes in Block and Inline Elements

The concept of "content-box" refers to the rectangular area that contains the text and any inner content of an element. Determining its height is crucial for achieving desirable layouts.

Block Elements

For block elements, the height of the content-box depends on two scenarios:

• Inline Formatting Context (IFC): When an element creates an IFC, the height is governed by line-boxes. Line-height defines the height of each line box, which collectively determine the content-box height. This applies to elements like

  and

  with line-height specified.
• Block Formatting Context (BFC): In a BFC, the height depends on the presence of block child elements, their margins, and potential margin collapsing. If there are block children, the height will extend to include them. If there are no block children, the height will be zero.

Inline Elements

In contrast to block elements, inline elements do not follow the same rules for content-box height. The specification intentionally leaves the height determination to the user agent (browser). The size of the content area is based on the font used.

While the user agent has flexibility in defining the height, it typically considers factors such as:

• Em-box Height: The height of the content area may be based on the em-box, ensuring consistent background styling relative to line-height.
• Glyph Ascents and Descenders: Alternatively, the height may be defined by the maximum ascender and descender of the font, accommodating glyphs that extend above or below the em-box.

It's important to note that inline elements generally do not obey height properties. Attempting to set an explicit height may not affect the content area size.

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