Let's Understand How EM and PX Works

In CSS, em and px are both units of measurement in CSS, but they differ significantly in how they determine the size of elements:

How EM Unit Works

The em unit is relative to the font size of the parent element. For example, if a parent element has a font size of 16 pixels and you set a child element's font size to 1em, it would be equivalent to 16 pixels. If you set the child element's font size to 2em, it would be double the font size of its parent, i.e., 32 pixels. em is useful for creating layouts that scale well across different screen sizes because it's relative to the font size, making it easier to maintain consistent proportions.

How PX Unit Works:

The px unit stands for pixels. It's an absolute unit of measurement, meaning it's fixed and not dependent on the size of any other element. One pixel represents one dot on a computer screen. Using px for sizing elements means they will have a fixed size regardless of the context or the size of the parent element's font. While px can provide precise control over element sizes, it doesn't scale well across different devices and can lead to layout issues on devices with different pixel densities.

Summarizing that em is relative and scalable, while px is absolute and fixed. The choice between them depends on the design requirements and the desired behavior of the elements in the layout. In modern web design, em (or rem, which is similar but relative to the root element) and other relative units are often preferred for their flexibility and responsiveness.