flex

A propriedade flex do CSS, define como um ítem será posicionado para no espaço disponível dentro de seu container.

Esta propriedade é uma abreviação das seguintes propriedades CSS:

• flex-grow (en-US)
• flex-shrink (en-US)
• flex-basis (en-US)

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
</div>

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item initial">initial</div>
  <div class="item initial">initial</div>
</div>

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
  <div class="item none">none</div>
</div>

<div class="flex-container">
  <div class="item initial">initial</div>
  <div class="item none">none</div>
  <div class="item none">none</div>
</div>

<div class="flex-container">
  <div class="item four">4</div>
  <div class="item two">2</div>
  <div class="item one">1</div>
</div>

* {
  box-sizing: border-box;
}

.flex-container {
  background-color: #F4F7F8;
  resize: horizontal;
  overflow: hidden;
  display: flex;
  margin: 1em;
}

.item {
  margin: 1em;
  padding: 0.5em;
  width: 110px;
  min-width: 0;
  background-color: #1B5385;
  color: white;
  font-family: monospace;
  font-size: 13px;
}

.initial {
  flex: initial;
}

.auto {
  flex: auto;
}

.none {
  flex: none;
}

.four {
  flex: 4;
}

.two {
  flex: 2;
}

.one {
  flex: 1;
}

/* Propriedades principais */
flex: auto;
flex: initial;
flex: none;

/* Valor único, sem unidade: flex-grow */
flex: 2;

/* Valor único, unidade width/height: flex-basis */
flex: 10em;
flex: 30%;
flex: min-content;

/* Dois valores: flex-grow | flex-basis */
flex: 1 30px;

/* Dois valores: flex-grow | flex-shrink */
flex: 2 2;

/* Três valores: flex-grow | flex-shrink | flex-basis */
flex: 2 2 10%;

/* Valores globais */
flex: inherit;
flex: initial;
flex: unset;

The flex property may be specified using one, two, or three values.

• One-value syntax: the value must be one of:
  • a <number>: In this case it is interpreted as flex: <number> 1 0; the <flex-shrink> value is assumed to be 1 and the <flex-basis> value is assumed to be 0.
  • one of the keywords: none, auto, or initial.
• Two-value syntax: the first value must be a <number> and it is interpreted as <flex-grow>. The second value must be one of:
  • a <number>: then it is interpreted as <flex-shrink>.
  • a valid value for width: then it is interpreted as <flex-basis>.
• Three-value syntax: the values must be in the following order:
  1. a <number> for <flex-grow>.
  2. a <number> for <flex-shrink>.
  3. a valid value for width for <flex-basis>.

initial

The item is sized according to its width and height properties. It shrinks to its minimum size to fit the container, but does not grow to absorb any extra free space in the flex container. This is equivalent to setting "flex: 0 1 auto".

auto

The item is sized according to its width and height properties, but grows to absorb any extra free space in the flex container, and shrinks to its minimum size to fit the container. This is equivalent to setting "flex: 1 1 auto".

none

The item is sized according to its width and height properties. It is fully inflexible: it neither shrinks nor grows in relation to the flex container. This is equivalent to setting "flex: 0 0 auto".

<'flex-grow'>

Defines the flex-grow (en-US) of the flex item. Negative values are considered invalid. Defaults to 1 when omitted.

<'flex-shrink'>

Defines the flex-shrink (en-US) of the flex item. Negative values are considered invalid. Defaults to 1 when omitted.

<'flex-basis'>

Defines the flex-basis (en-US) of the flex item. A preferred size of 0 must have a unit to avoid being interpreted as a flexibility. Defaults to 0 when omitted.

none | (en-US) [ (en-US) <'flex-grow'> (en-US) <'flex-shrink'> (en-US)? (en-US) || (en-US) <'flex-basis'> (en-US) ] (en-US)

#flex-container {
  display: flex;
  flex-direction: row;
}

#flex-container > .flex-item {
  flex: auto;
}

#flex-container > .raw-item {
  width: 5rem;
}

<div id="flex-container">
  <div class="flex-item" id="flex">Flex box (click to toggle raw box)</div>
  <div class="raw-item" id="raw">Raw box</div>
</div>

• CSS Flexbox Guide: Basic Concepts of Flexbox
• CSS Flexbox Guide: Controlling Ratios of flex items along the main axis