CSS 2.1 has four layout modes that can be strategically used, in addition to the ubiquitous floats. They are block layout, designed for laying out documents, inline layout, designed for laying out text, table layout, designed for laying out data in tabular format and positioned layout, designed for very explicit positioning without much regard for other elements in the document. Floats were originally applied to pictures so that they could be floated to the right or left and text would wrap around them. Both tables and floats have been used by web designers to create layouts for which they were never intended. Their use for layout is no longer necessary. Tables were replaced by floats in 2007 and floats were replaced by Flex and Grid in 2017.

CSS layout has been completely transformed by the release of multicolumn, flexbox and grid. CSS3 layout will be discussed next week.

Many layouts require multiple strategies at once. This means understanding all of the strategies. That needs to be the case in your final project.

The Box Model

The box model is central to understanding how to do layout with CSS. Every element is a content box with specific properties; padding, border and margin, in addition to all the other layout properties, like position, width, height, display, and so on.

The default setting for the box properties is zero, with the width set at 100% of the parent box. By default, all children boxes are the same width as their parent. A box that has the body element as parent is the width of the viewport/window.

In default behavior, specifying the width and hight of a box only specifies the width and height of the content. Padding, border and margins are in addition to the specified height and width. The actual size of the box in the layout is the content plus twice the margin, border and padding. A box that is 400px wide, with 20 px padding, 2 px border and 10px margins would take up 444 pixels.

Negative margins can be used to subtract from the space that the content takes up in the document flow. In the demo below, if the content is height: 300px, and has a margin-bottom: -150px, the next element down will start midway the box, because the negative margin does not effect the size of the content. Change the second box’s top and bottom margins to -75px; You will see the second box move up 75 points over the first box and the containing box’s size is reduced by 150px.

CSS 3 introduced the box-sizing property allowing box width to include the padding and borders. CSS Tricks has a nice history of how it ended up the way it is. It’s often applied to the entire page with the universal selector: *, *::before, *::after { box-sizing: border-box;}. You can toggle the box-sizing on and off in the demo or change it to content-box, the default, or padding-box:

Box Model Interactive

The Layout Modes

The layout modes determine the layout of boxes in the document flow. Boxes act either as block layout, like inline layout, like table layout or like positioned layout in which absolute and fixed positioning , which disregards the document flow.

The analogy that should resinate with most of you is to compare the document flow to the flow of a word processor, which starts at the top of the document and proceeds downward. Paragraphs are like block elements, meaning that if you give a style to a paragraph, it applies to the entire paragraph, even if you only selected part of it. When you apply a style to characters, on the other hand, only those characters selected receive the style.

Contrast this document flow with InDesign‘s ability to draw the box anywhere on the page. Each box, of course, initiates its own internal inline flow but the box itself is not connected to the document flow at all. That is how absolute and fixed positioning work.

This can warm design students to using the absolute positioning as the layout mode of choice but be forewarned. Web pages are not like printed pages, and as we shall see, it’s generally not a good idea to use absolute positioning as your main layout strategy.

That is because the elements are taken out of the document flow and no longer relate to one another. It may work for elements that do not change but if you are working with text, instead of pushing the remaining content down, it runs into it.

Tables, the forth layout mode, are in their own world, and wile they are great for tabular data, should not be used for layout purposes, as that violates the separation of church and state, eh, no, I mean, form and content.

Block Display

The block layout mode displays the boxes just described by the box model, in default configuration, as vertically , coming one after another down the page in the direction of the document flow. Each box, by default, is 100% the width of its parent. Even if the box is not 100% the width of its parent, block elements still start on a new line, by default, starting with the top left and corner of the <body> tag. Some HTML elements follow the block model by default, like headers <h1>, paragraphs <p> and list items<li>, and the generic block element, the <div>, though as we will see, their display quality can be changed to inline or table modes using the display property.

Inline Display

Inline tags enclose inline content elements. There are actually two kinds of inline content, replaced and non replaced elements. A character is an example of a non-replaced inline element, and a picture is an example of a replaced inline element. The box properties like margins, padding and border properties are applied differently to these elements.

Both of these kinds of inline elements flow one after one, till they reach the width of the containing box. The line then returns to the next line, just like this text. This inline flow, unlike the document flow, is language specific, and in the English language, the inline flow goes from left to right, repeating from top to bottom. In the Japanese language, the inline flow goes from top to bottom, repeating this from right to left.

Other elements whose default display is inline are the <img> tag, the Hyperlink <a> tag and the emphasis<strong>. The generic inline element is <span>, and you can use it to select any number of characters within the same parent container. The default inline display can be changed to block or table using the display property.

Tables

Tables themselves by default act like block elements but the layout mode of the table is different from the document flow. They used to be used for layout in the early days by programs like Dreamweaver created but they are not to be used for layout purposes anymore. Did I already say that?

The following example provides both the HTML used to build the table and the CSS used to style it. I have included the HTML code so that you can see their structure. The basic structure is a <table> element followed by a table row <tr>element in which table data <td> elements make up the columns. It is possible to nest tables, shown here by nesting the same table in two of the table data cells.

If you want to style the table, its best to create as many hooks in it as possible, and this table is loaded up with column descriptions, a table header, a table footer and multiple table bodies, all used in styling the table. The code and an explanation of how the table layout works is reproduced below:

<table id="table">
<caption>The Caption Holds the Title of the Table
</caption>
<col><col><col>
<thead> 
<tr><th>Head 1</th><th>Head 2</th><th>Head 3</th></tr>
</thead>
<tbody>
<tr> <td> table data </td>  <td> table data </td>  <td> table data </td></tr>
<tr> <td> table data </td>  <td> table data </td>  <td> table data </td></tr>
<tr> <td> table data </td>  <td> table data </td>  <td> table data </td></tr>
<tr> <td> table data </td> <td> table data </td> <td> table data </td></tr>
</tbody>
<tbody>
<tr> <td> table data </td>  <td> table data </td>  <td> table data </td></tr>
<tr> <td> TABLE </td>  <td> table data </td>  <td> TABLE </td></tr>
<tr> <td> table data </td>  <td> table data </td>  <td> table data </td></tr>
<tr> <td> table data </td> <td> table data </td> <td> table data </td></tr>
</tbody>
<tfoot>
<tr><td colspan="3">
	The Footer is a Place for Information About the Table.
</td></tr>
</tfoot>
</table>

For demonstration purposes, I included the table within itself, which is just a repeat of the code placed in a table data. The ability to put tables inside of tables for layout purposes was much abused in the early days of the web.

The HTML code for the table can be divided into parts, and each can be styled separately. There are table headings, footers, data cells and captions and rows, all of which can be styled. The even and odd table rows are styled using pseudo selectors. If you look at the code, you can see that the table caption comes first, then the table header, two table bodies that contain the table rows and the table data cells and finally a table footer. The row tags allow the three rows to be styled individually, though that too could be handled by pseudo selectors.

Positioning the Document Flow

All of the objects can be positioned in (or out of) the document flow, which stacks the content together like building blocks, only in reverse of gravity; starting at the top, the elements build their way down. W3.org talks of the way the elements flow on the page as the visual formatting model. These are the primary tools to create layout.

Normal Flow

In the normal flow, boxes are like blocks that follow the document flow as they stack. Each of these boxes can hold other boxes, inline content, or both.

Boxes are described as stacked paragraphs blocks, whereas inline elements are said to be “distributed in lines”.

Boxes can become inline elements when they are floated, and then act just like a character does in a line of text. Pictures act like inline content items as well but the boxes found in tables are another animal altogether, and follow the table construction rules.

The default normal flow of the boxes is like a word-processor, in which each box takes up space in the document flow. If top and bottom margins meet, they collapsed to the larger of the two margins as demonstrated above. Left and right margins never collapse, and auto margins suspend a child element horizontally centered in the containing element, also demonstrated above.

Relative Positioning

Relative positioning keeps the normal flow. The horizontal and vertical distance is shifted in relation to the position that the box has in the normal flow, and the space it occupied does not collapse. You can specify positive and negative distance from the top, left, bottom or right edges of the parent box. Boxes can and will overlap, and you use z-index to adjust which box is on top if you have specified a position. If the relative position distance is 0, there is no change from the static position. Notice that I have given the parent element a position of relative flow without deviation. Had I not done that, if I were to change the relative flow to absolute, the paragraphs would have ended up at the top of the page, rather than the top of the containing <div id="norm">Relative and Normal Position Interactive

Absolute Positioning

Absolute positioning is the forth layout mode, and it takes the box out of the normal document flow, except for a placeholder, the point of origin on which the absolute positioned box is aligned, and positions it in a layer above it in relation to the containing box’s coordinates, as long as that parent has been given a position in the document flow. If not, it continues on down the ancestry till it finds an element that has been given a position, or the body tag, which often happens, and which places the absolute value relative to the upper left hand corner of the window or viewport. To avoid this problem, remember to give the parent of the box you want to move absolutely a position: relative; without moving it from its place in the document flow.

There is an attraction for students to use absolute positioning as the main layout system since it follows the paradigm set up in print with programs like indesign. The problem is that the web is not like print, and such layouts quickly get into trouble. While it is fine to use absolute positioning for the very simplest of layouts, it breaks down for anything remotely more complicated, where it is a better idea to layout the document manipulating the document flow through margins, padding, floats and relative positioning.

These warnings aside, absolute positioning can be very useful in placing elements exactly where you need them, and can allow for some nifty layout calisthenics, as the demo shows, where objects are distributed by manipulating percentages in relation to the parent. If you change the position to fixed, the squares float in relation to the viewport. If you change the position to relative, and negate the object’s place in the normal document flow by adding negative margins, the objects will behave somewhat similar to the absolute positioned objects.

It is possible to manipulate elements like this because they can have more than one class as long as they are separated by a space: <div class="one box a">. Each box has three classes determining them: <div class="one box a"><p>1
</div>

Absolute Positioning Interactive

Fixed Positioning

Fixed position is a subcategory of absolute positioning. The difference being that the container box is the viewport. The viewport is the window, so it is absolutely fixed to the window, regardless of the scrolling contents in the window. This can be used for menus like the one to the right, that stays in place while the user scrolls up and down the page. You can see this if you change the position of the boxes above to fixed, and they will float in the relation to the viewport.

Sticky Positioning

CSS Positioned Layout Module Level 3 Sticky position is a hybrid position that incorporates elements of relative, absolute, and fixed positioning to accomplish its effect. When scrolling a page, an element sticks to the top or bottom for as long as the parent container element is visible.

When an element is defined as sticky, the parent element is automatically defined as the sticky container. The parent is the maximum area that the sticky item can float in. In the demo, the header only floats in the container designated by the green box, and has a z-index:10; stacking order, so it remains on top. The footer of the second box is also sticky.

Sticky Positioning Interactive

Z-Index Property

Once an element has been positioned, it’s overlap on the z-axis can be manipulated by the index property. This can be thought of in terms of having multiple layers, much like an Illustrator File. The normal flow happens at level 0, and you can put elements above and below the normal flow by giving them a number for −100 to 100.

Set the z-index of the following boxes to negative to read when using z-index can be useful. Play with the stacking order, and remember, the element you want to position in another layer other than the document flow has to be positioned first. Try giving the all the boxes a z-index of -3 and watch them move behind the text. Reverse the order of the boxes by changing the first box to -1, second to -2, third to -3 and the last box to -4.

Z-Index Property Interactive

Stacking Context

A stacking context is an element whose children can be ordered only relative to one another. Assigning the property z-index automatically creates a stacking context. As stacking contexts are not visually indicated there will be times when stacking contexts create confusion. It can happen, for example, that it becomes impossible to move one element on top of another using z-index despite astronomically high z-index values. As the z-index command does not work you may try to use !important to force it to work but to no avail. Once a stacking order is assigned to an element all its children become relative to each other and not relative to elements outside of the stacking order.

A number of other properties force stacking contexts because of the way CSS optimizes the way it renders a webpage. None of these properties are inherited but do pass on their effect to their children. These properties are opacity, transform, mix-blend-mode, perspective, isolation and position: fixed. The element and their children are flattened into a single layer to speed up rendering for browser efficiency. That makes it impossible to use z-index to layer something from outside the stacking context into any of those elements.

Display Property

The ability to change the display of an element is a very powerful feature of CSS, and its ability to function as a layout strategy has been overlooked during the time when floats reigned supreme as the Beyond Floats Article shows. It has since been updated to include flex and grid.

It is possible to change a block element to an inline element, to a list item to a table, table cell, etc. This is very useful for changing the basic behavior of an element exploited in the Beyond Floats Article.

Be aware that an inline object is content and does not have volume beyond the content box and requires the use of the inline-block value to change it to block behavior while remaining compatible with inline behavior.

Another important display values is display: none. That allows the element to be hidden from view till it is called up by a pseudo class like hover. This is one way to make CSS drop menus with multiple levels stay hidden till they are hovered over. No one here will build a website so complicated as to need such a menu though styling the navigation article demonstrates one. There is another property, visibility: hidden; or visibility: collapse;, that turns the visibility of objects on or off but that differs from display: none; in that the element still takes up room in the document flow.

Display Property Interactive

Overflow Property

Unless otherwise specified, each box will span the entire width of the parent and accommodate whatever content. If you specify a width, text will just wrap within that width but if a replaced element, like a picture or a video file, is larger than the specified width, it could overflow the box boundaries, it could be clipped at the box boundaries or it could be accommodated by specifying horizontal overflow, in which case a scrollbar would provide access to the otherwise clipped content.

If you specify a height, its possible that both pictures and text could force the content out of the box. You can control this though the overflow property, which allows you to control whether or not content remains visible, hidden or if scroll bars appear to facilitate the extra content. You can also specify which axis overflows. Take away the comments from overflow-x: hidden; and you will see the horizontal scroll bar disappear.

If a web site has both short and long documents, in which case the vertical scroll bar can appear and disappear from page to page, with the result that the web site re-centers and the jump is both undesirable and quite noticeable. Telling the HTML element to always scroll in the y axis can solve that problem overflow-y: scroll.

Overflow Property Interactive

Floated boxes

Floated boxes are part of the normal flow. When boxes are floated, they behave as inline elements. That means that they go from being in the document flow to being in the inline content flow of a parent box.

A box is either floated to the right or floated to the left, and it shifts the box to the right or left edge of the parent containing box at the line that the box is on. The remaining content then continues to flow around that box until it runs past the floated element or is cleared.

Floated boxes are central to multi-column page layouts, though that was not immediately apparent as they were first used to flow text around pictures. Nesting floats in one another is the basis for multi-column layouts. Nest one box inside of a floated box, and you have two columns, nest that box again inside another floated box, and you have three, and so on.

Floating Boxes Interactive

Floating Three Column Layout Interactive

A bulletproof three column layout.

<div>
<header>
HEADER
</header>
<aside>
SIDE A
</aside>
<article>
CONTENT
</article>
<aside>
SIDE B
</aside>
<footer>
FOOTER
</footer>
</div>
</div>

CSS3 Multi-Column Property

It is easy to create multi-column layouts using CSS3 multiple columns property. The document flow can create more columns inside a box than is visually pleasing, so change it to one, two, three or four columns, depending on the size of the screen. A good use of this would be in media queries, where small screens get one column, tablets get two and computer monitors get three or more columns.

Multi-Columns Interactive

CSS3 FlexBox Property

The Flexible Box Layout Module is designed solve a layout problem where the extra space is automatically divided between flexed siblings. It can align its contents horizontally or vertically, can have the order of the columns swapped dynamically, and can automatically “flex” the size of each columns to fit the available space. Flexbox demo. CSS-Tricks guide to Flexbox.

CSS3 Grid

The CSS Grid defines a two-dimensional grid-based layout system optimized for user interface design. In the grid layout model, the children of a grid container are positioned into arbitrary slots in a predefined flexible or fixed-size layout grid. Grid demo. CSS-Tricks guide to grid.