position

position 속성은 도큐먼트(document) 상에 요소를 배치하는 방법을 지정한다. top, right, bottom,  left 속성들은 요소가 최종적으로 배치될 위치를 지정한다.

/* Keyword values */
position: static;
position: relative;
position: absolute;
position: fixed;
position: sticky;
/* Global values */
position: inherit;
position: initial;
position: unset;

<div id="container">
  <div class="box"><strong>static</strong></div>
  <div class="box relative"><strong>relative</strong><br/><br/>top: 30px;<br/>right: 20px;</div>
  <div class="box sticky"><strong>sticky</strong><br/><br/>top: 20px;</div>
  <div class="box fixed"><strong>fixed</strong><br/><br/>left: 280px;</div>
  <div class="text">
    <p>Try scrolling this example to see the effect of
        <strong><code>fixed</code></strong> or
        <strong><code>sticky</code></strong> positioning.</p>
    <p>With <strong><code>fixed</code></strong> positioning, the
        element does not move as the viewport scrolls.</p>
    <p>With <strong><code>sticky</code></strong> positioning, the
        element moves until it reaches a threshold:
        in this case 20 pixels from the top of the container.</p>
    <p>The other two boxes show the effect of
        <strong><code>static</code></strong> and
        <strong><code>relative</code></strong> positioning.</p>  
  </div>
</div>

#container {
  border: 5px solid #F4F7F8;
  width: 100%;
  height: 300px;
  display: flex;
  overflow: scroll;
  box-sizing: border-box;
}
.box {
  height: 80px;
  margin: 5px;
  padding: 5px;
  margin-top: 100px;
  background-color: yellow;
  border: 2px solid red;
  color: red;
  font-family: monospace;
}
.text {
  max-width: 120px;
  padding: 0 0.5em 0 120px;
  font-family: sans-serif;
}
.relative {
  position: relative;
  top: 30px;
  right: 20px;
}
.sticky {
  position: sticky;
  top: 20px;
}
.fixed {
  position: fixed;
  left: 280px;
}

위치 지정(positioning)의 유형

• 배치된(positioned) 요소는 상대위치, 절대위치, 고정위치(fixed와 sticky)로 계산된 위치 값을 갖는다. (즉, static을 제외한 전부)
• A relatively positioned element is an element whose computed position value is relative. The top and bottom properties specify the vertical offset from its normal position; the left and right properties specify the horizontal offset.
• An absolutely positioned element is an element whose computed position value is absolute or fixed.The top, right, bottom, and left properties specify offsets from the edges of the element's containing block. (The containing block is the ancestor to which the element is relatively positioned.) If the element has margins, they are added to the offset.
• A stickily positioned element is an element whose computed position value is sticky. It's treated as relatively positioned until its containing block crosses a specified threshold, at which point it is treated as fixed.

Most of the time, absolutely positioned elements that have height and width set to auto are sized so as to fit their contents. However, non-replaced absolutely positioned elements can be made to fill the available vertical space by specifying both top and bottom and leaving height unspecified (that is, auto). They can likewise be made to fill the available horizontal space by specifying both left and right and leaving width as auto.

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.).

Syntax

The position property is specified as a single keyword chosen from the list of values below.

Values

static

The element is positioned according to the normal flow of the document. The top, right, bottom, left, and z-index properties have no effect. This is the default value.

relative

The element is positioned according to the normal flow of the document, and then offset relative to itself based on the values of top, right, bottom, and left. The offset does not affect the position of any other elements; thus, the space given for the element in the page layout is the same as if position were static. This value creates a new stacking context when the value of z-index is not auto. The effect of relative on table-*-group, table-row, table-column, table-cell, and table-caption elements is undefined.

absolute

The element is removed from the normal document flow; no space is created for the element in the page layout. Instead, it is positioned relative to its closest positioned ancestor if any; otherwise, it is placed relative to the initial containing block. Its final position is determined by the values of top, right, bottom, and left. This value creates a new stacking context when the value of z-index is not auto. Absolutely positioned boxes can have margins, and they do not collapse with any other margins.

fixed

The element is removed from the normal document flow; no space is created for the element in the page layout. Instead, it is positioned relative to the screen's viewport and doesn't move when scrolled. Its final position is determined by the values of top, right, bottom, and left. This value always creates a new stacking context. When an ancestor has the transform property set to something other than none, that ancestor is used as the container instead of the viewport (see CSS Transforms Spec). In printed documents, the element is placed in the same position on every page.

sticky 

The element is positioned according to the normal flow of the document, and then offset relative to its flow root and containing block based on the values of top, right, bottom, and left. The offset does not affect the position of any other elements. This value always creates a new stacking context. The effect of sticky on table-related elements is the same as relative. Note that sticky, by specification, will not work inside element with overflow: hidden or auto. (ref: Github issue on W3C CSSWG)

Formal syntax

static | relative | absolute | sticky | fixed

Examples

Relative positioning

Relatively positioned elements are offset a given amount from their normal position within the document, but without the offset affecting other elements. In the example below, note how the other elements are placed as if "Two" were taking up the space of its normal location.

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>

CSS

.box {
  display: inline-block;
  width: 100px;
  height: 100px;
  background: red;
  color: white;
}
#two {
  position: relative;
  top: 20px;
  left: 20px;
  background: blue;
}

Absolute positioning

Elements that are relatively positioned remain in the normal flow of the document. In contrast, an element that is absolutely positioned is taken out of the flow; thus, other elements are positioned as if it did not exist. The absolutely positioned element is positioned relative to its nearest positioned ancestor (i.e., the nearest ancestor that is not static). If a positioned ancestor doesn't exist, the initial container is used. In the example below, box "Two" has no positioned ancestor, so it is positioned relative to the the <body> of the document.

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>

CSS

.box {
  display: inline-block;
  width: 100px;
  height: 100px;
  background: red;
  color: white;
}
#two {
  position: absolute;
  top: 20px;
  left: 20px;
  background: blue;
}

Fixed positioning

Fixed positioning is similar to absolute positioning, with the exception that the element's containing block is the viewport. This can be used to create a floating element that stays in the same position regardless of scrolling. In the example below, box "One" is fixed at 80 pixels from the top of the page and 10 pixels from the left. Even after scrolling, it remains in the same place relative to the viewport.

HTML

<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

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

Sticky positioning

Sticky positioning can be thought of as a hybrid of relative and fixed positioning. A stickily positioned element is treated as relatively positioned until it crosses a specified threshold, at which point it is treated as fixed. For instance...

div { position: sticky; top: 10px; }

...would position a <div> relatively until the viewport were scrolled such that the element would be less than 10 pixels from the top. Beyond that threshold, the <div> would be fixed to 10 pixels from the top.

HTML

<dl>
  <div>
    <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>
  </div>
  <div>
    <dt>C</dt>
    <dd>Chromeo</dd>
    <dd>Common</dd>
    <dd>Converge</dd>
    <dd>Crystal Castles</dd>
    <dd>Cursive</dd>
  </div>
  <div>
    <dt>E</dt>
    <dd>Explosions In The Sky</dd>
  </div>
  <div>
    <dt>T</dt>
    <dd>Ted Leo &amp; The Pharmacists</dd>
    <dd>T-Pain</dd>
    <dd>Thrice</dd>
    <dd>TV On The Radio</dd>
    <dd>Two Gallants</dd>
  </div>
</dl>

CSS

* {
  box-sizing: border-box;
}
dl > div {
  background: #FFF;
  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;
  top: -1px;
}
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;
}

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] In Firefox 26 to Firefox 31 (inclusive), sticky positioning only works when the about:config preference layout.css.sticky.enabled is set to true. From Firefox 27 to 31, true is the default value for Nightly and Aurora versions of the browser. The preference has been removed in Firefox 48.

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

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

[5] Sticky positioning is in preview for Edge.