CSS Flex Box: How to vertically align “flex items” to middle without losing flex item height?

问题

Currently my "flex" items look like this (vertically aligned: top)...

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   1

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   2

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   3

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   4

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My Goal is to make them look like this (vertically aligned: middle)...

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   1
 _____________________________________

   2
 _____________________________________

   3
 _____________________________________

   4
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My requirements:

• The flex container must stay at 100% in height
• The flex items must stay 25% in height (equaling 100%, which is its default anyway).
• The flex items must be vertically centered.
• This must be responsive and be smart enough to stay in the middle per device (so no line-height/padding)

http://jsfiddle.net/oneeezy/p4XtA/

HTML

<!-- Flex Box -->
<section>

    <!-- Flex Items -->
    <div>1</div>
    <div>2</div>
    <div>3</div>
    <div>4</div>

</section>

CSS

/* Flex Box */
section { padding: 1em; background: black; display: flex; flex-flow: column; height: 100%; justify-content: space-around; }

/* Flex Items */
div { border-top: 1px solid #ccc; background: #f2f2f2; height: 25%; }
div:first-child { border-top: 1px solid transparent; }
div:hover { background: white; }

回答1:

Perhaps I'm misunderstanding, but can't you just do:

HTML (Slim)

.container
  .item 1
  .item 2
  .item 3
  .item 4

CSS

.container {
  display:flex;
  flex-direction: column;
  height: 100vh;
}
.item {
  flex-grow: 1;
  display:flex; 
  align-items:center;
  border-bottom:2px solid #e8e288;
}

Here's a Codepen

回答2:

To vertical align content of flexbox child, you will need to apply some other techniques.

I believe there will be content there , wrapped in tag, You can then again use flex and set child in margin:auto; DEMO

---

CSS updated :

/* Flex Box */
 section {
    padding: 1em;
    background: black;
    display: flex;
    flex-flow: column;
    height: 100%;
    justify-content: space-around;
}
/* Flex Items */
 div {
    border-top: 1px solid #ccc;
    background: #f2f2f2;
    height: 25%;
    display:flex;/* be a flexbox too */
}
div:first-child {
    border-top: 1px solid transparent;
}
div:hover {
    background: white;
}
p { /* or any child of flex box used */
    margin:auto;/* here center/middle align */
}

HTML structure :

<!-- Flex Box -->
<section>
    <!-- Flex Items , Flex Box themselves -->
    <div>
        <p style="width:100%;/* to fill entire width*/">1</p> <!-- Flex Items  -->
    </div>
    <div>
        <p>2</p><!-- Flex Items  -->
    </div>
    <div>
        <p>3</p><!-- Flex Items  -->
    </div>
    <div>
        <p>4</p><!-- Flex Items  -->
    </div>
</section>

---

Maybe a fallback with display:table , can be usefull : DEMO 2

/* fall back IE8 ie */
html, body, section {
    -moz-box-sizing:border-box;
    box-sizing:border-box;
    height:100%;
    width:100%;
}
section {
    display:table;
}
section > div {
    display:table-cell;
    vertical-align:middle;
}

/* Flex Box */
 section {
    padding: 1em;
    background: black;
    display: flex;
    flex-flow: column;
    height: 100%;
    justify-content: space-around;
}
/* Flex Items */
 section > div {
    border-top: 1px solid #ccc;
    background: #f2f2f2;
    height: 25%;
    display:flex;
}
section > div:first-child {
    border-top: 1px solid transparent;
}
section > div:hover {
    background: white;
}
p {
    margin:auto;
}

回答3:

Your problem is not really related to the so-called flex-box, in fact what you want to align is the content of the div (not the div), so just use some trick to align it normarlly. Here is one of the tricks:

div:before {
  content:'';
  height:100%;
  display:inline-block;
  vertical-align:middle;
}

Demo.

回答4:

This is the Flex-way of solving your problem:

HTML

<div style="height:300px;"> <!-- Just to test/change the height of <section> element -->
<!-- Flex Box -->
<section>
    <!-- Flex Items -->
    <div>1</div>
    <div>2</div>
    <div>3</div>
    <div>4</div>

</section>
</div>

CSS

/* Flex Box */
section {
    padding: 1em;
    background: black;
    display: flex;
    flex-flow: column;
    height:100%;
    justify-content: space-around;
}

/* Flex Items */
/* Child selector(>) is used to select <div> elements inside <section> element*/
section > div {
    border-top: 1px solid #ccc;
    background: #f2f2f2;
    height: 25%;

    /* Added code */
    display: flex;       /* Gives inner div flex display */
    align-items: center; /* Centers the div in the cross axis */
    /**************/
}
section > div:first-child {
    border-top: 1px solid transparent;
}
section > div:hover {
    background: white;
}

来源：https://stackoverflow.com/questions/23442692/css-flex-box-how-to-vertically-align-flex-items-to-middle-without-losing-flex