Baseline
The invisible line upon which most letters sit; the reference line for vertical alignment and rhythm in typography.
The baseline is the foundation of typographic layout. In CSS, text sits on the baseline of its line box. Vertical rhythm systems align baselines across columns and components so text feels evenly spaced.
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Anatomy of TypeRelated terms
X-Height
The height of lowercase letters such as x, a, and e, measured from the baseline to the top of the main body (excluding ascenders and descenders).
Ascender
The part of a lowercase letter that extends above the x-height, as in b, d, h, and l.
Descender
The part of a lowercase letter that extends below the baseline, as in g, j, p, q, and y.
Vertical Rhythm
A consistent vertical spacing system, often based on a baseline grid, that aligns text and UI elements across a layout.