Mobile-First CSS: Is It Time for a Rethink?

The mobile-first style approach is great—it focuses on what really matters to the consumer, it’s well-practiced, and it’s been a popular style design for years. But developing your CSS mobile-first should also be fantastic, too…right?

Well, not necessarily. Classic mobile-first CSS development is based on the principle of overwriting style declarations: you begin your CSS with default style declarations, and overwrite and/or add new styles as you add breakpoints with min-width media queries for larger viewports (for a good overview see “What is Mobile First CSS and Why Does It Rock?”). But all those exceptions create complexity and inefficiency, which in turn can lead to an increased testing effort and a code base that’s harder to maintain. Admit it—how many of us willingly want that?

Mobile-first CSS may yet be the best option for your own projects, but you need to first determine how ideal it is in light of the physical design and user interactions you’re working on. To help you get started, here’s how I go about tackling the elements you need to watch for, and I’ll discuss some alternative remedies if mobile-first doesn’t seem to fit your job.

Benefits of mobile-first

Some of the points to enjoy with mobile-first CSS growth —and why it’s been the de facto growth strategy for thus long—make a lot of feeling:

Development order. One thing you definitely get from mobile-first is a great development hierarchy—you only focus on the cellular view and get developing.

Tried and tested. It’s a tried-and-true method that has worked for years because it solves a problem actually also.

Prioritizes the smart see. The mobile view is the simplest and arguably the most significant because it covers all the crucial user journeys and frequently accounts for a higher proportion of user visits ( depending on the project ) ).

Stops desktop-centric growth. It can be tempting to first focus on the desktop perspective because enhancement is done using pc servers. However, considering mobile from the beginning prevents us from getting stuck eventually; no one wants to spend their time getting a site that is focused on desktops to operate on mobile devices!

Drawbacks of mobile-first

Model declarations can be set at lower breakpoints and finally overwritten at higher breakpoints:

More difficulty. The more unwanted script you inherit from lower thresholds, the higher up the order you go.

Higher CSS sensitivity. A school name declaration’s default style has then a higher specificity that has been returned to the browser’s default value. When trying to keep the CSS candidates as simple as possible, this can cause trouble on complex tasks.

Requires more analysis tests. All higher thresholds must be regression tested if modifications to CSS at a lower see ( such as adding a new style ) are to be made.

The browser can’t prioritize CSS downloads. At wider breakpoints, classic mobile-first min-width media queries don’t leverage the browser’s capability to download CSS files in priority order.

The issue of home value supersedes

Overwriting values is not necessarily essentially bad; CSS was created to do that. However, sharing incorrect values is counterproductive and can be burdensome and inadequate. When you have to replace styles to restore them to their defaults, which may cause issues after, especially if you are using a combination of bespoke CSS and power classes, it can also lead to more fashion specificity. We won’t be able to use a utility class on a style that has been increased in specificity when it was reset.

With this in mind, I’m developing CSS with a focus on the default values much more these days. Since there’s no specific order, and no chains of specific values to keep track of, this frees me to develop breakpoints simultaneously. I concentrate on finding common styles and isolating the specific exceptions in closed media query ranges (that is, any range with a max-width set).

This approach opens up some opportunities, as you can look at each breakpoint as a clean slate. If a component’s layout looks like it should be based on Flexbox at all breakpoints, it’s fine and can be coded in the default style sheet. However, if it appears that Grid is much better for large screens and Flexbox is much better for mobile, both can be accomplished entirely independently when the CSS is entered into closed media query ranges. Additionally, having a thorough understanding of any given component in all breakpoints upfront is necessary for developing simultaneously. This can help identify issues with the design more quickly in the development process. We don’t want to travel down the rabbit hole while creating complex mobile components, only to discover that the desktop designs are just as complex and incompatible with the HTML we created for the mobile view!

Though this approach isn’t going to suit everyone, I encourage you to give it a try. There are plenty of tools out there to help with concurrent development, such as Responsively App, Blisk, and many others.

Having said that, I don’t feel the order itself is particularly relevant. If you like to work on one device at a time, are comfortable with focusing on the mobile view, and have a good understanding of the requirements for other breakpoints, then you should definitely stick to the classic development order. The key is to find common styles and exceptions so that you can include them in the appropriate stylesheet, which is a manual tree-shaking procedure! Personally, I find this a little easier when working on a component across breakpoints, but that’s by no means a requirement.

Closed media query ranges in practice

In classic mobile-first CSS we overwrite the styles, but we can avoid this by using media query ranges. To illustrate the difference ( I’m using SCSS for brevity ), let’s assume there are three visual designs:

smaller than 768
from 768 to below 1024
1024 and anything larger

Take a simple example where a block-level element has a default padding of “20px,” which is overwritten at tablet to be “40px” and set back to “20px” on desktop.

Classic min-width mobile-first

.my-block { padding: 20px; @media (min-width: 768px) { padding: 40px; } @media (min-width: 1024px) { padding: 20px; }}

Closed media query range

.my-block { padding: 20px; @media (min-width: 768px) and (max-width: 1023.98px) { padding: 40px; }}

The subtle difference is that the mobile-first example sets the default padding to “20px” and then overwrites it at each breakpoint, setting it three times in total. In contrast, the second example sets the default padding to “20px” and only overrides it at the relevant breakpoint where it isn’t the default value (in this instance, tablet is the exception).

The goal is to:

Only set styles when needed.
Not set them with the expectation of overwriting them later on, again and again.

To this end, closed media query ranges are our best friend. If we need to make a change to any given view, we make it in the CSS media query range that applies to the specific breakpoint. We’ll be much less likely to introduce unwanted alterations, and our regression testing only needs to focus on the breakpoint we have actually edited.

Taking the above example, if we find that .my-block spacing on desktop is already accounted for by the margin at that breakpoint, and since we want to remove the padding altogether, we could do this by setting the mobile padding in a closed media query range.

.my-block {  @media (max-width: 767.98px) {    padding: 20px;  }  @media (min-width: 768px) and (max-width: 1023.98px) {    padding: 40px;  }}

The browser default padding for our block is “0,” so instead of adding a desktop media query and using unset or “0” for the padding value (which we would need with mobile-first), we can wrap the mobile padding in a closed media query (since it is now also an exception) so it won’t get picked up at wider breakpoints. At the desktop breakpoint, we won’t need to set any padding style, as we want the browser default value.

separating the CSS versus combining it

Due to the browser's concurrent request limit (typically around six ), it was crucial back then to keep the number of requests to a minimum. As a consequence, the use of image sprites and CSS bundling was the norm, with all the CSS being downloaded in one go, as one stylesheet with highest priority.

With HTTP/2 and HTTP/3 now on the scene, the number of requests is no longer the big deal it used to be. By using a media query, we can separate the CSS into several files. The obvious benefit of this is that the browser can now request the CSS it currently requires with a higher priority than the CSS it doesn't. This increases the speed at which pages are rendered more efficiently.

Which HTTP version are you using?

To determine which version of HTTP you're using, go to your website and open your browser's dev tools. Next, select the Network tab and check whether the Protocol column is visible. If "h2" is listed under Protocol, it means HTTP/2 is being used.

Note: to view the Protocol in your browser's dev tools, go to the Network tab, reload your page, right-click any column header ( e. g., Name ), and check the Protocol column.

Also, if your site is still using HTTP/1... WHY?!! What are you anticipating? The HTTP/2 user support is excellent.

Splitting the CSS

Separating the CSS into individual files is a worthwhile task. Linking the separate CSS files using the relevant media attribute allows the browser to identify which files are needed immediately (because they’re render-blocking) and which can be deferred. Based on this, it allocates each file an appropriate priority.

We can see that the mobile and default CSS are loaded with" Highest" priority in the following example of a website that is visited on a mobile breakpoint, since they are currently required to render the page. The remaining CSS files ( print, tablet, and desktop ) are still downloaded in case they'll be needed later, but with" Lowest" priority.

Before rendering can begin, the browser will need to download the CSS file and parse it using bundled CSS before rendering can begin.

While, as noted, with the CSS separated into different files linked and marked up with the relevant media attribute, the browser can prioritize the files it currently needs. Using closed media query ranges allows the browser to do this at all widths, as opposed to classic mobile-first min-width queries, where the desktop browser would have to download all the CSS with Highest priority. We can’t assume that desktop users always have a fast connection. For instance, in many rural areas, internet connection speeds are still slow.

Depending on project requirements, the media queries and the number of separate CSS files will vary from project to project, but the example below might look similar.

Bundled CSS

This single file contains all the CSS, including all media queries, and it will be downloaded with Highest priority.

Separated CSS

Separating the CSS and specifying a media attribute value on each link tag allows the browser to prioritize what it currently needs. Out of the five files listed above, two will be downloaded with Highest priority: the default file, and the file that matches the current media query. The others will be downloaded with Lowest priority.

Depending on the project’s deployment strategy, a change to one file (mobile.css, for example) would only require the QA team to regression test on devices in that specific media query range. Compare that to the prospect of deploying the single bundled site.css file, an approach that would normally trigger a full regression test.

Moving on

The adoption of mobile-first CSS was a significant development milestone because it allowed front-end developers to concentrate on mobile web applications rather than creating websites for desktop use and attempting to retrofit them to work on other devices.

I don't think anyone wants to return to that development model again, but it's important we don't lose sight of the issue it highlighted: that things can easily get convoluted and less efficient if we prioritize one particular device—any device—over others. For this reason, focusing on the CSS in its own right, always mindful of what is the default setting and what's an exception, seems like the natural next step. I've started to notice subtle simplifications in the CSS I write for myself as well as other developers, and that the testing and maintenance work is also a little more organized and effective.

In general, making CSS rule creation as simple as possible is ultimately a more effective strategy than moving around in circles of overrides. But whichever methodology you choose, it needs to suit the project. Mobile-first may—or may not—turn out to be the best choice for what's involved, but first you need to solidly understand the trade-offs you're stepping into.