Ah yes, CSS. Hardly a week passes without it being the topic of a heated online discussion. It’s too hard. It’s too simple. It’s unpredictable. It’s outdated. Peter Griffin struggles with blinds dot gif.
I don’t know why CSS sparks so many different emotions in developers, but I have a hunch as to why it can sometimes seem illogical or frustrating: You need a certain mindset to write good CSS.
Now, you probably need a mindset for coding in general, but the declarative nature of CSS makes it particularly difficult to grasp, especially if you think about it in terms of a “traditional” programming language.
Other programming languages often work in controlled environments, like servers. They expect certain conditions to be true at all times, and can therefore be understood as concrete instructions as to how a program should execute.
CSS on the other hand works in a place that can never be fully controlled, so it has to be flexible by default. It’s less about “programming the appearance” and more about translating a design into a set of rules that communicate the intent behind it. Leave enough room, and the browser will do the heavy lifting for you.
For most people who write CSS professionally, the mindset just comes naturally after a while. Many developers have that “aha!” moment when things finally start to click. It’s not just about knowing all the technical details, it’s more about a general sense of the ideas behind the language.
I tried to list some of these here.
Everthing is a Rectangle
This seems obvious, given that the box model is probably one of the first things people learn about CSS. But picturing each DOM element as a box is crucial to understanding why things layout the way they do. Is it inline or block level? Is it a flex item? How will it grow/shrink/wrap in different contexts?
Open your devtools and hover over elements to see the boxes they’re drawing, or use a utility style like
outline: 2px dotted hotpink to visualize its hidden boundaries.
The Cascade is your Friend
The Cascade - a scary concept, I know. Say “Cascade” three times in front of a mirror and somewhere, some unrelated styling will break.
While there are legitimate reasons to avoid the cascade, it doesn’t mean that it’s all bad. In fact, when used correctly, it can make your life a lot easier.
The important part is to know which styles belong on the global scope and which are better restricted to a component. It also helps to know the defaults that are passed down, to avoid declaring unnecessary rules.
As much as necessary, as little as possible
Aim to write the minimal amount of rules necessary to achieve a design. Fewer properties mean less inheritance, less restriction and less trouble with overrides down the line. Think about what your selector should essentially do, then try to express just that. There’s no point in declaring
width: 100% on an element that’s already block-level. There’s no need to set
position: relative if you don’t need a new stacking context.
Avoid unnecessary styles, and you avoid unintended consequences.
Shorthands have long effects
Some CSS features can be written in “shorthand” notation. This makes it possible to declare a bunch of related properties together. While this is handy, be aware that using the shorthand will also declare the default value for each property you don’t explicitly set. Writing
background: white; will effectively result in all these properties being set:
background-position: 0% 0%;
background-size: auto auto;
It’s better to be explicit. If you want to change the background color, use
Always Be Flexible
CSS deals with a large amount of unknown variables: screen size, dynamic content, device capabilities - the list goes on. If your styles are too narrow or restrictive, chances are one of these variables will trip you up. That’s why a key aspect in writing good CSS is to embrace its flexibility.
Your goal is to write a set of instructions that is comprehensive enough to describe what you want to achieve, yet flexible enough to let the browser figure out the how by itself. That’s why its usually best to avoid “magic numbers”.
Magic numbers are random hard values. Something like:
width: 218px; /* why? */
Whenever you find yourself tapping the arrow key in your devtools, adjusting a pixel value to make something fit - that’s probably a magic number. These are rarely the solution to a CSS problem, because they restrict styles to a very specific usecase. If the constraints change, that number will be off.
Instead, think about what you actually want to achieve in that situation. Alignment? An aspect ratio? Distributing equal amounts of space? All of these have flexible solutions. In most cases, it’s better to define a rule for the intent, rather than hard-code the computed solution to it.
Context is Key
For many layout concepts it’s imperative to understand the relationship between elements and their container. Most components are sets of parent and child nodes. Styles applied to the parent can affect the descendants, which might make them ignore other rules. Flexbox, Grid and
position:absolute are common sources of such errors.
When in doubt about a particular element behaving different than you’d want it to, look at the context it’s in. Chances are something in its ancestry is affecting it.
Content will change
Always be aware that what you see is just one UI state in a bigger spectrum. Instead of styling the thing on your screen, try to build a “blueprint” of the component. Then make sure that whatever you throw at it won’t break your styling.
Strings may be longer than intended or contain special characters, images might be missing or have weird dimensions. Displays may be very narrow or extremely wide. Those are all states you need to anticipate.
The number one mistake made by designers and developers alike is assuming that things will always look like they do in the static mockup. I can assure you, they will not.
Find Patterns and re-use them
When you set out to turn a design mockup into code, it’s often helpful to take inventory of the different patterns included first. Analyse each screen and take note of any concept that occurs more than one. It might be something small like a typographic style, or large like a certain layout pattern.
What can be abstracted? What’s unique? Thinking of pieces in a design as standalone things makes them easier to reason about, and helps to draw the boundaries between components.
Use consistent Names
A surprisingly large part of programming in general is coming up with good names for stuff. In CSS, it helps to stick to a convention. Naming schemes like BEM or SMACSS can be very helpful; but even if you don’t use them, stick to a certain vocabulary.
All these things were important for me to understand, but your personal experience as to what matters most might be different. Did you have another “aha” moment that made you understand CSS better? Let me know!