Bootstrap 3 vs Bootstrap 4 : Updates?

Bootstrap is a popular CSS Framework for making responsive websites and has been around for years. Most recently, Bootstrap 4, is finally released and ready for use. What are the differences between Bootstrap 3 and Bootstrap 4? Which version is more efficient for developers and clients? Is it worth the investment to migrate to the latest Bootstrap version, Bootstrap 4?


Bootstrap 4 is now using Flexbox as its layout mode. Flexbox, a one-dimensional layout model design and Grid for two-dimensional layouts, offers space distribution between interface items and awesome alignment abilities. The idea behind Flexbox’s layout is to give the container the ability to fill the remaining available space. Bootstrap’s new layout mode expands items to fill empty space or shrinks items to eliminate overflow.

Flexbox is not supported in IE 8 and 9 so Bootstrap 4 had to drop IE support. So if your project requires IE 8 and 9 support, you’ll want to install support.

5 Tier Grid System

The Bootstrap grid system improved from a 4 tier grid system to a 5 tier grid system. The additional breakpoint provides better support for devices with a screen size less than 576px, support for both portrait and landscape mode screen widths.

Less to Sass

Bootstrap 4 transitioned from Less to Sass as its CSS preprocessor. This advantageous move allows faster CSS compilation. Sass is papular for Front-End Developers because it’s ease of use and additional features that can help the developer work more efficiently.

em and rem Instead of Pixels as Primary CSS Units

The primary CSS units of Bootstrap 4 is now updated to em and rem instead of pixels. This will make it possible to implement responsive typography on Bootstrap sites and easily scale Bootstrap websites to all devices. It also increases the readability and accessibility of the code. Em and rem are flexible units that are converted into pixel values by the browser. The unit rem is relative to the font size of the root element of the page, that is, the HTML element. The global font size is 16 px. So that means 1 rem = 16 px. Since the unit is a relative unit it is easier to scale the layout up or down for devices. Em is also a relative unit but the difference is that em is relative to the font size of the element being styled upon.

Despite the switch, pixels are still used for media queries, grid breakpoints, and container widths as viewports are not affected by type size.


This is the definition of a Card from Bootstrap 4 docs:

“A card is a flexible and extensible content container. It includes options for headers and footers, a wide variety of content, contextual background colors, and powerful display options. If you’re familiar with Bootstrap 3, cards replace our old panels, wells, and thumbnails. Similar functionality to those components is available as modifier classes for cards.”

Updated Structures and Classes

  • Dropdown Structure – Can be created with “ul” or “div”.
  • Default Pagination – .page-item must be added to to each
  • element and .page-link to each “a” element.
  • Responsive images – Apply .img-fluid class
  • Responsive tables – .table-responsive class to be added to “table” element
  • Navbar alignment – Employ spacing utilities such as .mr-auto, or flexbox alignment


Utility Classes for faster mobile-friendly and responsive development Bootstrap 4 added dozens of utility classes to make the responsive development of your website faster. Utility classes are added to your containers to make it more efficient looking and you don’t have to adjust the padding and margins by yourself in every viewport but the utility classes will do it for you. For example, add responsive-friendly margin or padding values to an element using spacing utilities, flexbox utilities help you easily manage the layouts, sizing, and alignment, Display Property utilities help you to set elements of display property to block, inline or inline-block, change the alignment of elements using vertical alignment utilities, etc.


By default, Bootstrap 4 doesn’t have it’s own icon library but there are many to choose from. We recommend SVG implementations for their vector support and accessbility over other file formats.


Bootstrap 4 is stable now and it can make your work much faster using the built-in classes on it. To understand more about Bootstrap 4, check the documentation in their official website in how you can improve your typography, styles, and layouts of components in building mobile-friendly websites.

Geremy Gonzales

Geremy is a Web Developer at Project Assistant who specializes on front-end development. Most of the time he works on mobile responsive coding, making sure our websites are fluid and stay ship-shape in this vast modern mobile world. He’s also our go-to guy for email templates in MailChimp and Act-on.

He is a real funny guy with a great talent for making people laugh in the office. No one can hold back laughter when Geremy throws one of his jokes! He also loves to read Manga novels and watch anime episodes.