Designate is a WordPress plugin by Benedict Eastaugh that allows users to designate stylesheets to customise the appearance of their posts and pages.
There are two ways to use Designate: write stylesheets with names that correspond to the posts they're associated with, or choose a particular name by adding a custom field to your post or page.
Post stylesheets should be placed in the post-styles subdirectory of your
WP_CONTENT_DIR directory. Unless you have specified an alternative location
for your WordPress content directory, this will be
wordpress/wp-content/post-styles. All custom stylesheets must end in the
.css file extension.
By default Designate uses the permalink slug of a post to generate the name of
its custom stylesheet. For example, if a post has a permalink slug of
godels-incompleteness-theorems, the generated path will be
wordpress/wp-content/post-styles/godels-incompleteness-theorems.css
If you have several posts with the same permalink slug, you'll want to use post
IDs instead of permalink slugs to ensure that each post gets a unique
stylesheet name. To enable this option, change the DESIGNATE_USE_POST_SLUGS
constant in the plugin file from true to false.
This will give you stylesheets with names like the following (if e.g. the post
ID is 27)
wordpress/wp-content/post-styles/post-style-27.css
You can override either of these options at any time on an individual post or
page by adding a custom field to that post or page. The field should have a
name of stylesheet, and a value of the filename you wish to use. For example,
if you wanted to use a stylesheet called blue.css, you'd put blue.css as
the value of the custom field. Just blue would be fine too--the plugin will
sort out the file extension for you.