display: inline-flex does not make flex items display inline. It makes the flex container display inline. That is the only difference between display: inline-flex and display: flex. A similar comparison can be made between display: inline-block and display: block, and pretty much any other display type that has an inline counterpart.¹

There is absolutely no difference in the effect on flex items; flex layout is identical whether the flex container is block-level or inline-level. In particular, the flex items themselves always behave like block-level boxes (although they do have some properties of inline-blocks). You cannot display flex items inline; otherwise you don't actually have a flex layout.

It is not clear what exactly you mean by "vertically align" or why exactly you want to display the contents inline, but I suspect that flexbox is not the right tool for whatever you are trying to accomplish. Chances are what you're looking for is just plain old inline layout (display: inline and/or display: inline-block), for which flexbox is not a replacement; flexbox is not the universal layout solution that everyone claims it is (I'm stating this because the misconception is probably why you're considering flexbox in the first place).

¹ _{The differences between block layout and inline layout are outside the scope of this question, but the one that stands out the most is auto width: block-level boxes stretch horizontally to fill their containing block, whereas inline-level boxes shrink to fit their contents. In fact, it is for this reason alone you will almost never use display: inline-flex unless you have a very good reason to display your flex container inline.}

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OK, I know at first might be a bit confusing, but display is talking about the parent element, so means when we say: display: flex;, it's about the element and when we say display:inline-flex;, is also making the element itself inline...

It's like make a div inline or block, run the snippet below and you can see how display flex breaks down to next line:

.inline-flex { display: inline-flex; } .flex { display: flex; } p { color: red; }

Display Inline Flex

Display Flex

Also quickly create the image below to show the difference at a glance:

https://i.stack.imgur.com/mns2H.jpg

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flex and inline-flex both apply flex layout to children of the container. Container with display:flex behaves like a block-level element itself, while display:inline-flex makes the container behaves like an inline element.

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Using two-value display syntax instead, for clarity

The display CSS property in fact sets two things at once: the outer display type, and the inner display type. The outer display type affects how the element (which acts as a container) is displayed in its context. The inner display type affects how the children of the element (or the children of the container) are laid out.

If you use the two-value display syntax, which is only supported in some browsers like Firefox, the difference between the two is much more obvious:

display: block is equivalent to display: block flow

display: inline is equivalent to display: inline flow

display: flex is equivalent to display: block flex

display: inline-flex is equivalent to display: inline flex

display: grid is equivalent to display: block grid

display: inline-grid is equivalent to display: inline grid

Outer display type: block or inline:

An element with the outer display type of block will take up the whole width available to it, like <div> does. An element with the outer display type of inline will only take up the width that it needs, with wrapping, like <span> does.

Inner display type: flow, flex or grid:

The inner display type flow is the default inner display type when flex or grid is not specified. It is the way of laying out children elements that we are used to in a <p> for instance. flex and grid are new ways of laying out children that each deserve their own post.

Conclusion:

The difference between display: flex and display: inline-flex is the outer display type, the first's outer display type is block, and the second's outer display type is inline. Both of them have the inner display type of flex.

References:

The two-value syntax of the CSS Display property on mozzilla.org

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The Difference between "flex" and "inline-flex"

Short answer:

One is inline and the other basically responds like a block element(but has some of it's own differences).

Longer answer:

Inline-Flex - The inline version of flex allows the element, and it's children, to have flex properties while still remaining in the regular flow of the document/webpage. Basically, you can place two inline flex containers in the same row, if the widths were small enough, without any excess styling to allow them to exist in the same row. This is pretty similar to "inline-block."

Flex - The container and it's children have flex properties but the container reserves the row, as it is taken out of the normal flow of the document. It responds like a block element, in terms of document flow. Two flexbox containers could not exist on the same row without excess styling.

The problem you may be having

Due to the elements you listed in your example, though I am guessing, I think you want to use flex to display the elements listed in an even row-by-row fashion but continue to see the elements side-by-side.

The reason you are likely having issues is because flex and inline-flex have the default "flex-direction" property set to "row." This will display the children side-by side. Changing this property to "column" will allow your elements to stack and reserve space(width) equal to the width of its parent.

Below are some examples to show how flex vs inline-flex works and also a quick demo of how inline vs block elements work...

display: inline-flex; flex-direction: row;

Fiddle

display: flex; flex-direction: row;

Fiddle

display: inline-flex; flex-direction: column;

Fiddle

display: flex; flex-direction: column;

Fiddle

display: inline;

Fiddle

display: block

Fiddle

Also, a great reference doc: A Complete Guide to Flexbox - css tricks

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Display:flex apply flex layout to the flex items or children of the container only. So, the container itself stays a block level element and thus takes up the entire width of the screen.

This causes every flex container to move to a new line on the screen.

Display:inline-flex apply flex layout to the flex items or children as well as to the container itself. As a result the container behaves as an inline flex element just like the children do and thus takes up the width required by its items/children only and not the entire width of the screen.

This causes two or more flex containers one after another, displayed as inline-flex, align themselves side by side on the screen until the whole width of the screen is taken.

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You can display flex items inline, providing your assumption is based on wanting flexible inline items in the 1st place. Using flex implies a flexible block level element.

The simplest approach is to use a flex container with its children set to a flex property. In terms of code this looks like this:

.parent{
   display: inline-flex;
}

.children{
   flex: 1;
}

flex: 1 denotes a ratio, similar to percentages of a element's width.

Check these two links in order to see simple live Flexbox examples:

https://njbenjamin.com/bundle-3.htm https://njbenjamin.com/bundle-4.htm

If you use the 1st example:

https://njbenjamin.com/flex/index_1.htm

You can play around with your browser console, to change the display of the container element between flex and inline-flex.

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You need a bit more information so that the browser knows what you want. For instance, the children of the container need to be told "how" to flex.

Updated Fiddle

I've added #wrapper > * { flex: 1; margin: auto; } to your CSS and changed inline-flex to flex, and you can see how the elements now space themselves out evenly on the page.

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I'd like to add some details about screen reader behaviour, because there's some surprises here.

Some background first. Some screen readers like NVDA handle display: block and display: inline-block differently (and they should, as you will see later).

Comparison between different display attributes

display: block

A display: block element will always be announced in a separate "line", meaning NVDA will stop talking after its contents, and the user will manually tell NVDA to announce the next element (typically with Down arrow key).

<div>This is the first line</div>
<div>This is another line</div>

This will make NVDA announce This is the first line, and then This is another line.

The following yields the same result:

<span style="display: block">This is the first line</span>
<span style="display: block">This is another line</span>

display: inline-block

A display: inline-block element will be announced together with all preceding and following other inline elements (display: inline and display: inline-block).

<span style="display: inline-block">This is the first line</span>
<span style="display: inline-block">This is another line</span>

This will make the screen reader announce both elements in one go: This is the first line This is another line.

As said before, it doesn't matter whether it's an inline or inline-block element; the following yields the exact same result:

<span style="display: inline">This is the first line</span>     <!-- Inline! -->
<span style="display: inline-block">This is another line</span> <!-- Inline block! -->

display: flex

This works exactly like display: block.

display: inline-flex

Surprisingly, this also works like display: block, not like display: inline-block!

display: grid / display: inline-grid

I didn't test this, but I expect the same like with flex / inline-flex here.

Why is that a problem?

Using display: inline-block, one can create elements that visually look very distinct, but semantically are treated "as one".

For example, consider the following headline in an online news platform:

<h2>
  <span class="category">Rain forests</span>
  They need our love
</h2>

You now want to visually style the category (Rain forests) very different to the "real" title ('They need our love'), i.e. by putting each in its own line, something like this:

https://i.stack.imgur.com/flRdg.png

If you'd make category a display: block element, then the screen reader would announce the heading in two separate lines like this: Rain forests, heading level 2, then They need our love, heading level 2. This is confusing to the user: are there two different headings on the page? Why is there no content for the first one (instead, immediately an apparent second heading seems to follow)?

If however you'd make category a display: inline-block element, then the screen reader would announce the heading in one go: Rain forests They need our love, heading level 2.

It is sad, that display: inline-flex (and probably inline-grid, too) does not mimic the behaviour. So if you want to offer perfect accessibility, you might want to use inline-block in such situations.

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Open in Full page for better understanding

.item { width : 100px; height : 100px; margin: 20px; border: 1px solid blue; background-color: yellow; text-align: center; line-height: 99px; } .flex-con { flex-wrap: wrap; /* */ display: flex; /* 1. uncomment below 2 lines by commenting above 1 line */ /* */ /* display: inline-flex; */ } .label { padding-bottom: 20px; } .flex-inline-play { padding: 20px; border: 1px dashed green; /* */ width: 1000px; /* */ display: flex; }

Flex vs inline-flex

This pen is understand difference between flex and inline-flex. Follow along to understand this basic property of css

• Follow #1 in CSS:
  • Comment display: flex
  • Un-comment display: inline-flex
• Hope you would have understood till now. This is very similar to situation of `inline-block` vs `block`. Lets go beyond and understand usecase to apply learning. Now lets play with combinations of A, B, C & D by un-commenting only as instructed:
  • A with D -- does this do same job as display: inline-flex. Umm, you may be right, but not its doesnt do always, keep going !
  • A with C
  • A with C & D -- Something wrong ? Keep going !
  • B with C
  • B with C & D -- Still same ? Did you learn something ? inline-flex is useful if you have space to occupy in parent of 2 flexboxes .flex-con. That's the only usecase

Playground:

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