CSS Only Themes: A regular WordPress theme normally comes with a design for the public facing side of a WordPress website (the front-end) and some unique functionality (e.g. widget areas, menus, options etc) for the admin area. A Micro Theme just affects the front-end design. Nothing else. So theme specific widgets, menus, and options are left untouched.
Micro Themes provide a way to customize WordPress Themes without actually modifying the Theme’s files in any way. A Micro Theme transforms the look of a Theme by contributing additional CSS styles that work in harmony with the Theme’s existing CSS styles. In this respect, a Micro Theme is like a tailor made plugin for a specific WordPress theme.
Child Themes vs Micro Themes: You might be thinking that Micro Themes sound similar to Child Themes, and they are, but there’s a crucial difference. All the (CSS) styles that produce the front-end design of a Micro Theme are easily editable via a WordPress admin screen (the Microthemer UI). So while regular WordPress themes (or child themes) sometimes have a few customisation options, Micro Themes are inherently customisable.
So Micro Themes actually serve two purposes. They (i) provide an alternative design or “skin” for a Theme and, when used in conjunction with Microthemer (as opposed to Microloader), they (ii) provide users with design editing options so extensive they make most Theme Options want to run into the corner and shut their eyes. For users that just want to customize WordPress themes without loading someone else’s alternative “skin”, Themeover provides FREE Blank Slate Micro Themes.
Terminology: There are actually 4 types of Micro Theme: Blank Slate Micro Themes, Plugin Styles, Graphics Packs, and of course regular old Micro Themes. Only the latter is referred to just as a Micro Theme (the type this page is mostly talking about), but from a technical point of view, all types are the same. They are a collection of files in a directory. And they are all installed in the same way. However, they all have different uses and so they are given different names.
A Brief Technical Overview of Micro Themes
User-friendly CSS Generator: Micro Themes are created with Microthemer. Microthemer allows Micro Theme authors to define CSS selectors in a semi-hidden way so that non-technical end users can just modify CSS property values (via select menus and colour pickers). This is what makes Micro Themes so appealing. With a Micro Theme, Non-technical users have the ability to apply different styles to a selection of predefined elements (that have user friendly labels) without the chore of learning code. With Microthemer and Micro Themes, users can customize WordPress themes with a similar degree of control that CSS savy web designers enjoy.
External Stylesheet: When an end user activates a Micro Theme, an external CSS file is generated in the following directory: wp-content/micro-themes/active-styles.css. This CSS file is included in the head section of the html document, after the theme’s default styles.css file. This is how the Micro Theme overrides the theme’s default CSS rules. Note: it doesn’t override the stylesheet entirely. It just contains certain CSS selectors that are more specific than those in style.css.
Manageable Number of Styles: Because a Micro Theme doesn’t totally replace the parent theme’s CSS, it doesn’t need to contain as many style rules. This makes it easier to keep the number of customisable styles down to a manageable amount. That’s not to say that Micro Themes are thin on styling options though. Some Micro Themes provide options for styling over 400 web page elements!
Authoring Micro Themes: Creating a saleable Micro Theme with Microthemer is really easy. It’s best to grab a free Blank Slate Micro Theme from our repository to serve as a starting point. Once you’ve defined your CSS override styles for a given parent theme (via the Microthemer UI), all you need to do is fill out the meta information, enter any instructions in the Readme textarea, create a screenshot thumbnail of your Micro Theme (220px x 165px), and then export your Micro Theme as a zip file. Users who download your Micro Theme from the Themeover marketplace, will be able to edit all the CSS style rules you defined via the Microthemer UI.