What is `rem` vs `em` vs `px` and when to use each

rem, em, px, CSS units, web design, responsive design
Learn the differences between rem, em, and px units in CSS and when to use each for better responsive web design.

In web design, units of measurement are crucial for defining the size of elements. Here’s a breakdown of the three most commonly used CSS units: rem, em, and px.

Pixels (px): Pixels are absolute units that define a specific amount of space on the screen. They are fixed and do not change based on other elements. Use px for precise control over layout.

Em (em): The em unit is relative to the font-size of the element. For example, if an element’s font-size is 16px, 1em will equal 16px. If you set the size of a child element to 2em, it will be twice the font size of its parent.

Rem (rem): The rem unit is relative to the root element (usually the <html> element). If the root font-size is 16px, 1rem will always equal 16px regardless of the parent element’s font size. Use rem for consistent sizing across a web page.

Here is a simple example of how to use these units in CSS:

            .container {
                font-size: 16px; /* 1rem = 16px */
            }
            .box {
                width: 300px; /* fixed width in pixels */
                padding: 2em; /* padding based on the font-size of its parent */
                margin: 1rem; /* margin based on the root font-size */
            }

rem em px CSS units web design responsive design

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