Two specific files control the landing page experience for logged-in and logged-out users. Essential Files for Theme Development
Create a manifest.xml (or elgg-plugin.php in newer versions) to define the theme's name, version, and author. CSS Customization: Elgg 1.9 Themes
According to customization tutorials from Packt , these are the primary components of an Elgg theme: File/Folder Contains all decorations, colors, and font definitions. Pageshell Two specific files control the landing page experience
To change styles, you can override elements/layout/columns.css by copying the core file to your plugin's views/default/elements/layout/ directory. Elgg 1.9 Themes
This default theme introduced a fresher color palette and a layout designed to work across desktop and mobile screens. Step-by-Step: Creating a Basic Theme Plugin