Relative Sizing

"rem" stands for "root em," and it is a relative unit that is based on the font size of the root element. This means that when you set a size in "rem," it will be relative to the base font size, making it adaptable to changes in font size. This is particularly useful for creating responsive designs that can scale with user preferences.

Accessibility

Using "rem" units makes it easier to create accessible websites. Users with visual impairments can adjust their browser's font size, and your layout will respond accordingly if you've used "rem" units consistently.

Easy to Scale

"rem" units can be scaled up or down globally by changing the font size on the root element. This can help in creating a consistent and scalable design without having to manually adjust every element size.

Maintenance

When you use "rem" units, you can maintain a more consistent and predictable sizing system throughout your CSS. This can make it easier to manage and update your styles, as changes to the root font size will affect the entire design.

Flexibility

"rem" units provide more flexibility in terms of design. You can define font sizes, margins, padding, and other dimensions using "rem," which will respond to changes in font size settings. This can be particularly useful when working with complex layouts.

Future-Proofing

As web standards evolve and devices with varying screen resolutions become more common, using "rem" units can help ensure your design remains adaptable to different contexts.

While "rem" has several advantages, it's important to note that there are scenarios where "px" may still be appropriate, such as when you need to create fixed-size elements that should not change based on font settings. Additionally, it's common to use a combination of both "rem" and "px" units in a CSS stylesheet to take advantage of the benefits of each in different parts of the design.