What's the difference between display:inline-flex and display:flex?

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.}

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;
}

<body>
  <p>Display Inline Flex</p>
  <div class="inline-flex">
    <header>header</header>
    <nav>nav</nav>
    <aside>aside</aside>
    <main>main</main>
    <footer>footer</footer>
  </div>

  <div class="inline-flex">
    <header>header</header>
    <nav>nav</nav>
    <aside>aside</aside>
    <main>main</main>
    <footer>footer</footer>
  </div>

  <p>Display Flex</p>
  <div class="flex">
    <header>header</header>
    <nav>nav</nav>
    <aside>aside</aside>
    <main>main</main>
    <footer>footer</footer>
  </div>

  <div class="flex">
    <header>header</header>
    <nav>nav</nav>
    <aside>aside</aside>
    <main>main</main>
    <footer>footer</footer>
  </div>
</body>

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

display flex vs display inline-flex

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.

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

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

What's the difference between display:inline-flex and display:flex?

Using two-value `display` syntax instead, for clarity

Outer display type: `block` or `inline`:

Inner display type: `flow`, `flex` or `grid`:

Conclusion:

References:

Related

Recent Posts

What's the difference between display:inline-flex and display:flex?

Using two-value display syntax instead, for clarity

Outer display type: block or inline:

Inner display type: flow, flex or grid:

Conclusion:

References:

Related

Recent Posts

Using two-value `display` syntax instead, for clarity

Outer display type: `block` or `inline`:

Inner display type: `flow`, `flex` or `grid`: