position

Resumo

A propriedade position em CSS define alternativas para posicionar elementos, projetados para serem úteis em efeitos de animações.

Um elemento posicionado é um aquele cuja posição computada será uma dentre: relative, absolute, fixed ou sticky.

Um elemento posicionando relativamente é aquele cuja posição foi configurada como relative.

Um elemento posicionado absolutamente é aquele cuja posição foi configurada como absolute ou fixed.

Um elemento posicionado como "pegajoso" é aquele cuja posição foi configurada como sticky.

As propriedades top, right, bottom, e left especificam a posição que elementos dispostos em tela terão.

Sintaxe

/* Valores Chave */
position: static;
position: relative;
position: absolute;
position: fixed;
position: sticky;

/* Valores Globais */
position: inherit;
position: initial;
position: unset;

Valores

static

Faz o elemento ter um comportamento normal, que é o de manter sua posição atual no fluxo da página.  As propriedades top, right, bottom, left e z-index não se aplicam para elementos com posição static.

relative

This keyword lays out all elements as though the element were not positioned, and then adjust the element's position, without changing layout (and thus leaving a gap for the element where it would have been had it not been positioned). o efeito de da posição relativa em elementos table-*-group, table-row, table-column, table-cell, e table-caption é indefinida.

absolute

Do not leave space for the element. Instead, position it at a specified position relative to its closest positioned ancestor or to the containing block. Absolutely positioned boxes can have margins, they do not collapse with any other margins.

fixed

Do not leave space for the element. Instead, position it at a specified position relative to the screen's viewport and don't move it when scrolled. When printing, position it at that fixed position on every page. This value always create a new stacking context.

sticky 

The box position is calculated according to the normal flow (this is called the position in normal flow). Then the box is offset relative to its flow root and containing block and in all cases, including table elements, does not affect the position of any following boxes. When a box B is stickily positioned, the position of the following box is calculated as though B were not offset. The effect of ‘position: sticky’ on table elements is the same as for ‘position: relative’.

Formal syntax

static | relative | absolute | sticky | fixed

Exemplos

Posicionamento relativo

Conteúdo HTML

<div class="box" id="one">One</div>
<div class="box" id="two">Two</div>
<div class="box" id="three">Three</div>
<div class="box" id="four">Four</div>

Conteúdo CSS

.box { 
   display: inline-block; 
   background: red; 
   width: 100px; 
   height: 100px; 
   float: left; 
   margin: 20px; 
   color: white; 
}

#two { 
   position: relative; 
   top: 20px; 
   left: 20px; 
}

Note how the other elements are displayed as if "Two" were in its normal position and taking up space.

Live sample of relative positioning

Posicionamento Absoluto

Elements that are positioned relatively are still considered to be in the normal flow of elements in the document. In contrast, an element that is positioned absolutely is taken out of the flow and thus takes up no space when placing other elements. The absolutely positioned element is positioned relative to nearest positioned ancestor(non static). If a positioned ancestor doesn't exist, the initial container is used.

In the example below, a positioned ancestor doesn't exist and box Two is positioned absolutely relative to initial container:

HTML Content

<div class="box" id="one">One</div>
<div class="box" id="two">Two</div>
<div class="box" id="three">Three</div>
<div class="box" id="four">Four</div>

CSS Content

.box { 
   display: inline-block; 
   background: red; 
   width: 100px; 
   height: 100px; 
   float: left; 
   margin: 20px; 
   color: white; 
}

#two { 
   position: absolute; 
   top: 20px; 
   left: 20px; 
}

Live sample of absolute positioning

If box One had not been positioned relative, it would not be the nearest positioned ancestor, and so box Two would have appeared relative to the upper left corner of the outer box instead.

Fixed positioning

Fixed positioning is similar to absolute positioning, with the exception that the element's containing block is the viewport. This is often used to create a floating element that stays in the same position even after scrolling the page. In the example below the "One" box is fixed 80px from the top of the page and 20px from the left:

HTML Content

<div class="outer">
  <p>
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam congue tortor eget pulvinar lobortis.
    Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Nam ac dolor augue.
    Pellentesque mi mi, laoreet et dolor sit amet, ultrices varius risus. Nam vitae iaculis elit.
    Aliquam mollis interdum libero. Sed sodales placerat egestas. Vestibulum ut arcu aliquam purus viverra dictum vel sit amet mi.
    Duis nisl mauris, aliquam sit amet luctus eget, dapibus in enim. Sed velit augue, pretium a sem aliquam, congue porttitor tortor.
    Sed tempor nisl a lorem consequat, id maximus erat aliquet. Sed sagittis porta libero sed condimentum.
    Aliquam finibus lectus nec ante congue rutrum. Curabitur quam quam, accumsan id ultrices ultrices, tempor et tellus.
  </p>
  <p>
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam congue tortor eget pulvinar lobortis.
    Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Nam ac dolor augue.
    Pellentesque mi mi, laoreet et dolor sit amet, ultrices varius risus. Nam vitae iaculis elit.
    Aliquam mollis interdum libero. Sed sodales placerat egestas. Vestibulum ut arcu aliquam purus viverra dictum vel sit amet mi.
    Duis nisl mauris, aliquam sit amet luctus eget, dapibus in enim. Sed velit augue, pretium a sem aliquam, congue porttitor tortor.
    Sed tempor nisl a lorem consequat, id maximus erat aliquet. Sed sagittis porta libero sed condimentum.
    Aliquam finibus lectus nec ante congue rutrum. Curabitur quam quam, accumsan id ultrices ultrices, tempor et tellus.
  </p>
  <div class="box" id="one">One</div>
</div>

CSS Content

.box {
  background: red;
  width: 100px;
  height: 100px;
  margin: 20px;
  color: white;
}
#one {
  position: fixed;
  top: 80px;
  left: 10px;
}
.outer {
  width: 500px;
  height: 300px;
  overflow: scroll;
  padding-left: 150px;
}

When viewing the top of the page, the position box appears in the upper left, and after scrolling, it remains in the same place relative to the viewport:

Live sample of fixed positioning

Sticky positioning

Sticky positioning is a hybrid of relative and fixed positioning.  The element is treated as relative positioned until it crosses a specified threshold, at which point it is treated as fixed positioned.  For instance:

#one { position: sticky; top: 10px; }

will behave just like a relatively positioned element until the viewport scrolls such that the element would be less than 10px from the top.  Then, it will be fixed to 10px from the top until the viewport is scrolled back past this threshold.

HTML Content

<div>
  <dl>
    <dt>A</dt>
    <dd>Andrew W.K.</dd>
    <dd>Apparat</dd>
    <dd>Arcade Fire</dd>
    <dd>At The Drive-In</dd>
    <dd>Aziz Ansari</dd>
  </dl>
  <dl>
    <dt>C</dt>
    <dd>Chromeo</dd>
    <dd>Common</dd>
    <dd>Converge</dd>
    <dd>Crystal Castles</dd>
    <dd>Cursive</dd>
  </dl>
  <dl>
    <dt>E</dt>
    <dd>Explosions In The Sky</dd>
  </dl>
  <dl>
    <dt>T</dt>
    <dd>Ted Leo & The Pharmacists</dd>
    <dd>T-Pain</dd>
    <dd>Thrice</dd>
    <dd>TV On The Radio</dd>
    <dd>Two Gallants</dd>
  </dl>
</div>

CSS Content

dl {
  margin: 0;
  padding: 24px 0 0 0;
}

dt {
  background: #B8C1C8;
  border-bottom: 1px solid #989EA4;
  border-top: 1px solid #717D85;
  color: #FFF;
  font: bold 18px/21px Helvetica, Arial, sans-serif;
  margin: 0;
  padding: 2px 0 0 12px;
  position: -webkit-sticky;
  position: sticky;
  width: 99%;
  top: 0px;
}

dd {
  font: bold 20px/45px Helvetica, Arial, sans-serif;
  margin: 0;
  padding: 0 0 0 12px;
  white-space: nowrap;
}

dd + dd {
  border-top: 1px solid #CCC
}

Notes

For relatively positioned elements, the top or bottom property specifies the vertical offset from the normal position and the left or right property specifies the horizontal offset.

For absolutely positioned elements, the top, right, bottom, and left properties specify offsets from the edge of the element's containing block (what the element is positioned relative to). The margin of the element is then positioned inside these offsets.

Most of the time, absolutely positioned elements have auto values of height and width computed to fit the contents of the element. However, non-replaced absolutely positioned elements can be made to fill the available space by specifying (as other than auto) both top and bottom and leaving height unspecified (that is, auto). Likewise for left, right, and width.

Except for the case just described of absolutely positioned elements filling the available space:

• If both top and bottom are specified (technically, not auto), top wins.
• If both left and right are specified, left wins when direction is ltr (English, horizontal Japanese, etc.) and right wins when direction is rtl (Persian, Arabic, Hebrew, etc.).

Specifications

Browser compatibility

[1] Since Firefox 30, Gecko allows <tr>, <thead>, and  <tfoot> elements with a position: relative; style to act as absolute positioning containers. This means that a position: absolute; styled element inside the table can be positioned relative to these elements. In other browsers and in older versions of Firefox, setting position: relative; on a table row or row group has no effect. Firefox helps developers transition to the new behavior and detect any rendering issues it may cause on their sites by printing a warning to the JavaScript console if you use this feature: Relative positioning of table rows and row groups is now supported. This site may need to be updated because it may depend on this feature having no effect.

[2] Sticky positioning only worked in Firefox 26 to Firefox 31, included, when the about:config preference layout.css.sticky.enabled is set to true. From Firefox 27 to 31, it was the default value for Nightly and Aurora versions of the browser.

[3] In Internet Explorer, fixed positioning doesn't work if the document is in quirks mode.

[4] Support for sticky positioning was removed in Chrome 23, but there is plan to support it in the future.

[5] Prior to Firefox 44, position: fixed didn't created a stacking context in most cases. The specification, and Gecko implementation, have been modified to mimick Chrome and Safari long time behavior.

[6] Sticky positioning is under consideration for Edge