Should I use px or rem value units in my CSS?

Delving into px and rem

Why px?

Pixels (px) are like the boulders of the web. They're solid, they're dependable and they don't move an inch (or a pixel).

• Absolute, unyielding control? You want px.
• Want crisp and clear images, borders and a resolution-independent design? px is your guy.
• Living in the past with legacy browsers (looking at you, IE 😄)? Stick with the familiar px.

And why rem?

Enter the rem unit. Psychedelic compared to the sober pixel, rem is related to the root element's font size. It's flexible, modern and your go-to for:

• Accessibility: Adjusting font sizes for visually impaired users? rem is your friend.
• Scalability: Want your website to be comfortable on any screen size? Make rem the lynchpin and see it shine.
• Easier maintenance: Change your mind often? Use rem for easier updates to text and layout.

px meets rem: a thrilling saga

In the stylish world of CSS, mixing px and rem brings old and new together, leading to a beautiful cocktail of flexibility and control:

.element {
  margin: 20px; /* for our elders */
  margin: 2.5rem; /* for the cool kids */
}
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Frameworks like Bootstrap 4 have embraced rem as the future of scalable layouts.

It's not all sunshine and rainbows 🌈☔

Keep an eye out for oddities like Safari's font-size bug involving media queries and rem. Otherwise, you might get a nasty surprise.

Tools to Help You Decide

Simplifying with CSS Preprocessors

Modern preprocessors like Sass or Less are wizards in taming rem and px. Define variables or mixins, make your media queries neat and tidy, and bring order to the chaos of unit conversion:

$baseFontSize: 16px; // The One Ring to rule them all

@mixin font-rem($size) {
  font-size: ($size * 1px); // Set in stone
  font-size: ($size / $baseFontSize) * 1rem; // Aim for the stars
}
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Dynamic scaling

Harness the power of rem by adjusting the root font-size for site-wide scaling:

html { font-size: 125%; } // We're going bigger!
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Remember the User

Unit selection should put user experience front and center. Always consider user-adjustable settings like zoom and font-size preferences. Adaptable and change-loving, rem is a winner for user-focused design.