30px

30px is a length unit used in CSS to specify measurements in CSS pixels. A CSS pixel is a unit that maps to device pixels through the device pixel ratio, so on standard displays 1 CSS pixel equals 1 device pixel, while on high-density screens it can correspond to more than one device pixel. The 30px value therefore represents a fixed visual length in the CSS layout, independent of the physical screen resolution.

It is commonly used for typography, spacing, and element dimensions. For example, font-size: 30px sets display-size text; width: 30px and height: 30px define small blocks; margins and paddings can also be specified in px.

Because px is an absolute unit in CSS, it interacts with relative units like rem and em; on a page with a root font size of 16px, 30px equals 1.875rem.

Designers should consider accessibility and responsiveness; fixed px sizes may hinder scaling for users who need larger text; combining px with media queries or using relative units improves adaptability.

In practice, 30px is a common choice for noticeable but compact elements across web interfaces.