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What is rem in CSS?​

In CSS , the rem unit is a relative length unit that stands for "root em." It is relative to the font-size of the root element of the document, which is typically the <html> element. Unlike the em unit, which is relative to the font-size of the element itself (or its parent, depending on the context), the rem unit is always relative to the root element's font-size.

When you see 2.4 rem in CSS, it means that the size (whether it be font-size, margin, padding, etc.) is 2.4 times the font-size of the root <html> element. For example, if the font-size of the <html> element is set to 16 pixels (which is a common default in browsers), then 2.4 rem would be equivalent to 2.4 * 16 = 38.4 pixels.

This unit is particularly useful for creating scalable and responsive designs, as it allows you to define sizes that are consistent and relative to a single base value set at the root level. Changing the font-size of the root element can then scale up or down the size of all elements defined with rem units throughout the document.