Viewport Units in CSS

Published in

YoungInnovations' Blog

4 min readMar 8, 2017

Over past few years, Responsive design has become quite the hot topic in the web design community. There are various frameworks which help to build responsive design faster. One of the ways is using Viewport percentage units or “Viewport Units” for short, a CSS3 property which helps you to automate some aspects of your responsive design.

Using viewport units, the size of specific elements can adapt to the varying size of a browser.

Instead of pixel, em or percentage values, you can use these settings:

vw: the percentage of the browser’s width
vh: the percentage of the browser’s height
vmin: the minimum percentage of browser’s height or width, the smallest value of both
vmax: the maximum percentage of browser’s height or width, the smallest value of both

You may use these units in any CSS property that accepts values in px such as width, height, margin, font-size, etc. They will be recalculated by the browser on window resize or device rotation.

Let’s take an overview of its advantages:

Full Height of the page

Traditionally, we have been using height:100% to get full height of the container to fit on the screen. We can obtain the same result with less code by using vh. This helps to scale an image to the height of the user’s screen. View demo in codepen. To see a difference, replace 100vh with 100% in the Codepen demo.

.image-container {
  height: 100vh;
  width: auto;
}

Keeping an element shorter than the screen

This technique can be useful if you want to explicitly control the height of an element relative to the viewport size so that it will always remain in view. View demo in codepen

.shortme {
  max-height: 80vh;
}

Scaling Text (Responsive text)

Using this technique it gives developers great flexibility when adjusting font sizes and they help to scale dynamically with the viewport size. For easy practice place a base font size in the root element, and then use a viewport unit on the root element’s font size, and scale with that.

Media queries combine nicely with vw units to ensure readability across various screen sizes. View demo in codepen. Try changing a base font size (html) value.

html {
  font-size: 20px;
}

h1 {
  font-size: calc(100% + 5vw); 
}

Breaking out of the container

Viewport units make it possible to break outside of a containing element or elements. In scenarios where the CMS makes it difficult or impossible to alter our markup in an HTML template, using viewport units can achieve the desired result regardless of the markup. This technique won’t work in every scenario, but it’s a nice trick in some instances. View demo in codepen

.container {
  max-width: 1024px;
  margin: 0 auto;
}

.breakout { 
  position: relative;
  left: 50%;
  transform: translate(-50%, 0);
  width: 100vw; 
}

Browser Support

As you can see, there’re solid supports for viewport units across all major web browsers. You may run across few bugs though. It is always a good practice to check caniuse before implementing a newer technique in your design.

Conclusion

By coming this far I hope you are already loving Viewport Units. And personally, I can say viewport units are perfect fit to a wide range of devices. I suggest you to give it a try in your project, explore and enjoy!

I hope you’ve found this blog very helpful. Feel free to share your thoughts and opinions and leave me a comment if you have any problems or questions.