Is changing default display property a good practice?

Question

TL;DR Is it a bad practice to change default display property in my CSS?

Issue

Recently, in our project we had to position 2 header tags so they would look like one. They had the same font size and similar styling so the only issue was how to place one next to another. We had 2 different ideas on that and it le do a discussion on whether or not is a good practice to change default display property

So, our very basic code

<div class="container">
    <h1>Header:</h1>
    <h2>my header</h2>
</div>

The outcome we would like to have:

Header: my header

Note: The code needs to consists of 2 different headings because on mobile version we want to display them in in separate lines (so leaving default display: block).

Approach #1: Use display: inline

This is pretty stright forward. Block elements became inline so they are positioned in the same line. The disadvantage of this approach is that default display properties of both h1 and h2 were changed.

Approach #2: Use float

H1 can be positioned on the left using float: left property. This approach leaves the default display property intact, but will requires some hacks if the .container is not long enough to fit both headers in single line.

The question

It all leads to a simple question: Is it a bad practice to change the default display property of HTML elements? Is it breaking the standard and should be avoided if possible? Or is it our bread and butter and it does not really matter, as long as code is semantically correct (so headers are placed in h1, articles are placed in article etc...)

Answer 1

Answering your main question:

tl;dr is it a bad practice to change default display property in my CSS?

NO

---

WHY?

A: Because it is all about semantics

Elements, attributes, and attribute values in HTML are defined (by this specification) to have certain meanings (semantics). For example, the ol element represents an ordered list, and the lang attribute represents the language of the content.

These definitions allow HTML processors, such as Web browsers or search engines, to present and use documents and applications in a wide variety of contexts that the author might not have considered.

---

So, in your case if you really need to have 2 headings semantically then you can change their styles, including the display property.

However If you don't need to have 2 headings semantically, but only for purely cosmetics/design (responsive code), then you are doing it incorrectly.

Look at this example:

<h1>Welcome to my page</h1>
<p>I like cars and lorries and have a big Jeep!</p>
<h2>Where I live</h2>
<p>I live in a small hut on a mountain!</p>

Because HTML conveys meaning, rather than presentation, the same page can also be used by a small browser on a mobile phone, without any change to the page. Instead of headings being in large letters as on the desktop, for example, the browser on the mobile phone might use the same size text for the whole the page, but with the headings in bold.

This example has focused on headings, but the same principle applies to all of the semantics in HTML.

** Emphasis in the quote above is mine **

P.S - Remember that headings h1–h6 must not be used to markup subheadings (or subtitles), unless they are supposed to be the heading for a new section or subsection.

---

With all this above in mind, here is a few (good) approaches:

If you're doing the two headings purely for design then:

• add a span inside of the h1, using a media query either using mobile first approach (min-width) or the non-mobile approach (max-width).

PROs - easily manageable through CSS, changing only properties.

CONs - adding extra HTML markup, using media queries as well.

h1 {
  /* demo only */
  background: red;
  margin:0
}
@media (max-width: 640px) {
  span {
    display: block
  }
}

<div class="container">
  <h1>Header:<span> my header</span></h1>
</div>

If you need to use the two headings semantically then:

• use flexbox layout.

PROs - no need to add extra HTML markup or the use of media queries, being the most flexible currently in CSS (basically the cons from option above mentioned).

CONs - IE10 and below has partial or none support, Can I use flexbox ? (fallback for IE10 and below would be CSS TABLES)

.container {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  /*demo only*/
  background: red;
}

h1,
h2 {
  /*demo only*/
  margin: 0;
}

h2 {
  /*640px will be flex-basis value - can be changed as prefered */
  flex: 0 640px;
}

<div class="container">
  <h1>Header:</h1>
  <h2>my header</h2>
</div>

Sources:

• W3C specs - 3.2.1 Semantics
• W3C specs - 4.12.1 Subheadings, subtitles, alternative titles and taglines

Answer 2

tl;dr is it a bad practice to change default display property in my CSS?

No. As expressed by W3C themselves; HTML conveys meaning, not presentation.

As an HTML author, it's your job to structure a page so that every section of the page carries the intended semantics as described by the documentation, so that software (browsers, screen readers, robots...) can correctly interpret your content.

As a CSS author, it's your job to alter the default styling of correct markup to present it the way you want to. This includes changing the default display properties just as much as changing the default color.

Any software can, however, decide that certain usage of CSS properties changes the way they interpret your page. For instance, a search engine could decide that text that has the same color as their parent's background should carry no weight for their ranking system.

In regards to subheadings, it's considered incorrect to markup a subheading with an <hX> element. What you should do is to decide on one <hX> element, wrap it in a <header> and wrap subheading-type text in <p>, <span> or similar.

The following is an example of proper subheadings, taken from the W3C documentation:

<header>
  <h1>HTML 5.1 Nightly</h1>
  <p>A vocabulary and associated APIs for HTML and XHTML</p>
  <p>Editor's Draft 9 May 2013</p>
</header>

Note that there's a discrepancy between the W3C specification and the WHATWG specification where the latter uses the <hgroup> element for this specific purpose, while the former has deprecated it. I personally go with W3C's example, but most software will still understand hgroup, likely for many, many years to come, if you prefer the WHATWG approach. In fact, some argue that WHATWG should be followed over W3C when the specs differ.

In your particular example, however, I'm not sure why you chose to split the <h1> into two elements in the first place. If what you marked up as an <h1> is actually supposed to be a generic "label" for the heading, then it should probably be considered a subheading instead. If you need to split it for styling purposes, wrap the two parts of text in <span> as such:

<h1>
  <span>Header:</span>
  <span>my header</span>
</h1>

Answer 3

tl;dr is it a bad practice to change default display property in my CSS?

Its a good practice but choose carefully when to use it because it can cause some critical structure mistakes.

Why is it a good practice

The display property is open for changes. It makes HTML simple and generic. HTML elements come with a default display value that match the general behavior - what you would usually want. But they dont have to be kept and manipulated around to imitate another display property. Think about <div> for example. Obviously most of the times you want it to have display: block;, but display: flex; is much more suitable once in a while.

Lets look at a really common example of lists. <li> comes with the display property of list-item that breaks the lines for every new item.

<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ul>

But horizontal lists are very common too. So why there is no special element for horizontal list items? Writing a special element for every common display behavior adds complexity. Instead, the convention, as also suggested by W3C is to set the <li> display property to inline.

ul li {
  display:inline;
}

<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ul>

display: inline-block; as an alternative to float

float has been used massively in page layout for many years. The problem is that it wasnt created for this task and was originally designed to wrap text around elements. A well-known float issue is that non floated elements dont recognize floated children because they are being removed from the normal flow of the document. You also cannot centrally float an element. you are limited to left or right floats only.

display is much more suitable for layout many times. display: inline-block; tells browsers to place that element inline, but to treat it as though it were a block level element. This means that we can use inline-block instead of floats to have a series of elements side by side. It is more intuitive and eliminates floats <div class="clearfix"></div> which is an additional non semantic element in your HTML.

Floats are useful when there is a need to float an element so that other page content flows around it. But there is no need to always press them into the service of a complicated layout.

Things to avoid when changing display

When you change the display property remember:

Setting the display property of an element only changes how the element is displayed, NOT what kind of element it is.

<span> test case:

In HTML early versions <span> is considered an inline-level element and <div> is block-level. Inline-level elements cannot have block-level elements inside them. Giving the <span> a display:block; doesn't change his category. It is still an inline-level element, and still cannot have <div> inside.

HTML5 introduced content models. Each HTML element has a content model: a description of the element's expected contents. An HTML element must have contents that match the requirements described in the element's content model. <span> can contain only phrasing content. It means that still you cannot nest a <div> (flow content) inside a <span>. Giving <span> a display:block; still doesn't change it.

Avoid:

span {
  display:block;
}

<span>
  <div>
    Still Illegal!
  </div>
<span>

In conclusion, changing the default display property is certainly our bread and butter. Remember that it only changes how the element is displayed, NOT what kind of element it is and use it correctly.

Now about the original two heading issue:

With respect to the comments:

Let's assume for the sake of the question, that we need to have two headings. Or let's forget about the headings for the time being. - by the author

And also to the comment:

This question is not about resetting the display value globally. Using selectors to target only the specific elements is implied. The question is what we should do with these elements once selected. - by the person who set the bounty

Two headings side by side not only to handle mobile layout changes, can be done in many ways. The original example is simple and correct so its actually a good way.

h1, h2 {
  display: inline;
}

<div class="container">
    <h1>Header:</h1>
    <h2>my header</h2>
</div>

It follows HTML rules and doesnt require any additional hacks.