A while back a custom theme I designed for a client disappeared from the theme manager in WordPress admin section and instead of displaying the custom design WordPress resorted back to one of the default themes. The theme files were all correct and present on the server and so far as I could see everything else such as file permissions were all in order, but after a bit of digging I found the resolution.
There are a few reasons a custom WordPress theme may not show up, or may disappear from the admin section; you have to define your theme properly at the top of your theme stylesheet; file permissions can cause issues and I’ve also experienced issues when removing all other (unused) themes from the theme folder (older versions of WordPress had problems when there was only one theme in the themes folder).
However if you’ve used WordPress themes before and you’re confident the above issues are all in order yet you’re still not seeing your theme files then you may be left scratching your head. I was.
However after a bit of digging I discovered that post version 3.0 WordPress are ‘Deprecating overly minimal themes’.
As a result, if your custom theme doesn’t include any of the following theme files:
header.php, footer.php, sidebar.php, comments.php, comments-popup.php
then WordPress will revert to the default theme.
Considering my client’s website was effectively ‘down’ (i.e. displaying a default version of WordPress which would have been confusing visitors) I needed the quickest dirtiest fix to get it sorted.
My resolution was to copy all of my custom theme files into the default theme folder overwriting any existing duplicates, but keeping any files in the default folder that did not exist in my custom theme. I then uploaded this to the server and hey presto my custom design was back online!
If you have the time I would definitely recommend doing the opposite – figure out which files are missing from your custom theme folder and then copy and paste them from the default folder in order to get your theme working.
For further info on why your theme might not be showing up take a look at http://westi.wordpress.com/2010/05/03/themes-and-wordpress-3-0-some-important-changes/ or for more info on designing and developing custom themes here’s a useful checklist from WordPress.org http://codex.wordpress.org/Theme_Development#Template_File_Checklist
This post was written by WillyNilly