CSS flex

CSS flex allows us to position elements more easily, simplifying webpage layouts using only CSS.

We could look at elements as either being a flex container or a flex item.

Flex containers

To make an element a flex container (also known as a flex wrapper), we would add display: flex in its CSS:

.flex-wrapper {
  display: flex
}

Then, we would apply it in its corresponding HTML tag:

<div class="flex-wrapper">
  <!-- this is now a flex container -->
</div>

Inline-flex

Using display: inline-flex creates a container that won't take up the full-width, so elements can exist beside the container:

.flex-inline-wpr { 
  display: inline-flex
}

.non-flex-inline-wpr {
  display: inline
}

The .flex-inline-wpr would then allow any .non-flex-inline-wpr to appear beside (instead of under) the former:

<div class="flex-inline-wpr">
  <!-- this is now a flex container -->
</div>

<div class="non-flex-inline-wpr">
  <!-- this can appear beside flex-wpr instead of under -->
</div>

Items within a container using display: inline-flex would also still enjoy display: flex type properties!

Flex container properties

(In each of these properties, we must have display: flex or display: flex-inline before we use the following!)

Horizontal alignment

We use the justify-content property with the following values:

• flex-start
  • child items appear at the beginning (by default, on the left)
• flex-end
  • child items appear at the end (by default, on the right)
• center
  • child items appear in the middle
• space-around
  • child items appear evenly spaced out, with automatic margins on the left and the right
• space-between
  • child items appear evenly spaced out, but with no margins on the left and the right

Vertical alignment

We use the align-items property with the following values:

• flex-start
  • child items appear at the top (by default)
• flex-end
  • child items appear at the bottom (by default)
• center
  • child items appear equally between the top and the bottom

Notice how we say "by default" as rotational transformations (i.e. a flip) can also occur whereby flex-start applies to the bottom and flex-end applies to the top of the element!

Re-sizing items

The following properties have to do with the sizes of an element's child items, but they are applied in the element itself:

• flex-grow
  • lets the items grow for large window sizes
    • positive numeric value x sets it to x times the default
• flex-shrink
  • lets the items shrink for small window sizes
    • positive numeric value x sets it to 1/x times the default
• flex-basis
  • lets the items grow/shrink with an absolute limit
    • i.e. a positive numeric value of pixels

Re-arranging items

The following properties have to do with the order of an element's child items, but they are applied in the element itself:

• flex-direction
  • row
    • items are arranged from left to right, from the top left
  • row-reverse
    • items are arranged from right to left, from the top right
  • column
    • items are arranged from the top to bottom, from the top left
  • column-reverse
    • items are arranged from the bottom to top, from the bottom right
• flex-wrap
  • wrap
    • items are put in a new line if no space remains
  • wrap-reverse
    • items are also put in a new line, but in reverse order
  • nowrap
    • items will not wrap
• flex-flow
  • combines the flex-direction and flex-wrap in one property
    • e.g. flex-flow: column wrap