css-position

Have you ever wonder how display properties make an HTML element flow? Most of the layout models like box-model, flex-mode, and float-model use a Static Flow. meaning all the elements will take up space in the browser window as defined by its flow model. To make it understandable, All elements will flow on the page as they are defined in browser style. Elements like div will use full-width space, elements like strong, em, span, p will use inline flow.

Sometimes we have to put element out of the flow and sometimes move in the flow. We can do that using position property and some helper properties. We can simply set position values to static, relative, absolute, fixed or sticky to achieve this. All these property values behave differently in terms of flow. Let's discuss how to use display properties like a pro in this article.

CSS syntax:

Selector{ position: <value>;}

Javascript syntax

document.getElementById('selector').style.position = "<value>";

<value> : can be either static, relative, absolute, sticky, fixed

We can categorise these values into two groups. Values that put element out of flow and values that do not put element out of the flow. When you set one position value and try to switch it between other values, you'd see other elements jumping around. That behaviour is because some values move elements out of the flow.

When an element is moved in or out of the flow, there are some helper properties that we can use to place the element at its desired position. Those helper properties are :

  • top: valid positive width value
  • left: valid positive width value
  • right: valid positive width value
  • bottom: valid positive width value
  • z-index: valid integer value

Using Helper Properties:

When these properties are used with a relative, absolute, fixed they move an element to the desired point on the screen from the top and left corner. This behaviour is also dependent on its closest related child if not the body. I use a combination of two properties like ( top and left ) or ( top and right ) or (bottom and left) or (bottom and right).

There is a reason I avoid using opposite properties, mainly because it can create confusion while using absolute positioning. Results may differ on different screen sizes. The majority of the time, using the top will make the bottom ineffective, and using the left will make the property right ineffective.

The bottom and right properties will be ignored if height and property are set. Making the element snap to the top-left end. Try the below example to understand problems that might occur due to using opposite properties. Try checking any opposite properties and observer how the bounding box is not sitting inside the box.

When two or more elements are moved in or out of the flow, they might overlap with each other. The simple solution to arrange them in the correct depth is by using z-index. However z-index property has more complex usage when using multiple layers.

Now let's look at the position values and how they affect the flow of the layout.

Throughout the article, we'll use the same html structure as defined:

<div class="room">
<div class="bed"></div>
<div class="bed"></div>
<div class="bed"></div>
<div class="bed"></div>
<div class="kid bed-pos"></div>
<div class="bed"></div>
<div class="bed"></div>
</div>
</div>

We'll change the position of .kid class and observer the various behaviours.

Using CSS Position Property

position: static

This is the default value of position when we don't specify anything. This position will take up the needed space and keep the layout in-flow.

For example, try to GRAB THE SLEEPWALKING CHILD. Observe, helper properties change when you grab the element. But visually there is no change. This is because helpers don't work on static positions for all browsers.

position: relative

Just in addition to static positions, relative positions make helper properties work. In other words, top, left, right, bottom properties will start to affect the layout when a position is relative.

The element moves into a specified position because of helpers which are out-flow behaviour but, by moving this relative position element, we are not adjusting or removing its original space occupied. Meaning, there will be a blank spot at the object's static position. This is in-flow behaviour. So relative acts as in-flow as well as out-flow.

In the below example, try to move the kid element with the mouse, Viola.

You will be able to move the element from the original position keeping the static space intact even after dragging the element. The static position is shown as a dotted line in the demo

position: absolute

When a position is set to absolute, it will take the element out-flow and the static space occupied by the positioned element will be collapsed. The absolutely positioned element will move with respect to its closest relative parent, the document itself otherwise.

In the below example, observe the bounding rectangle, the space of the walking child in the earlier example is occupied by the next element. This is the normal behaviour of the absolutely positioned elements.

This property allows the designer to manipulate elements as needed because of its out-flow behaviour. Helper properties will work the same as defined above.

position: fixed

Fixed positioned elements share the same properties as absolute in terms of flow and helper properties. Meaning, It will move element out of the flow, the element can be moved using helper properties. But these elements will stay in their position even after page scrolling.

Fixed is a relative killer because its coordinates don't really react with respect to any relatively positioned element. The element will place itself with reference to the entire document.

Until…

It has an ancestor with a transform, perspective, or filter property set to anything other than none. If you have any container with the above properties enabled, The element will position itself inside the container losing its ability to stay fixed on scroll.

Try the above example, The kid element is fixed. It has a parent container with position:relative. Grab the kid, Observe, the element coordinate reacts to the document and not a relative parent.

position: sticky

In addition to the fixed positioned element, Think of sticky as a combination of both fixed and relative.

Only top and left helper property work with a sticky position. When any helper property is set with sticky, the element will move up-down or side-by-side when you scroll. The element will stat fixed within its related parent.

In the below example, try to scroll the window both horizontally and vertically. Grab the child and move it around and check scrolling again. Observe, The element never goes out of its relatively positioned element. Even after specifying higher values than the container, it will stay inside the container.

There you have it. I have covered the most useful CSS positioning with examples.

Final Thoughts:

It's no wonder most of the web uses statically positioned elements. Some enhancements are made over time by UI developers to various components of the site using absolutely and fixed positioned element. We see positioned elements in various UI elements. To name a few multi-level navigations, sticky menus, overlaid element, cards, lightboxes, chatboxes and many more. The position is too small of a property but once you know the fundamentals of each type, you'd be able to solve many complex problems and develop more complex layer-based designs.

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