To install items via the "Install" button, you can either use OCS-URL (see below) or the Opendesktop.org App:
The App comes with OCS-URL included, so clicking on the "Install" button downloads, extracts and copies a file to the appropriate theme location of most Linux Desktop Environments and Distros.
OCS-URL - Browser Protocol Extension
OCS-URL allows easy distro-independent installation of themes, wallpapers, etc. under most desktop environments by simply clicking on the "Install" button. (Note: You can use the Opendesktop.org-App if you don't want to install this extra).
Video Installation Guide
Here is a video how to install ocs-url program:
To install ocs-url program, get the package from here: https://www.linux-apps.com/p/1136805/
After ocs-url program is installed, you can click any "Install" button on openDesktop.org. Only supported filetypes have an "Install" button.
If you use Firefox, a program selection window opens the first time you click on an Install button: Choose "ocs-url" as custom URL handler and tick "remember the file association".
If you don't get the program selection window or you are using another browser, please set the ocs-url program as custom URL handler for ocs:// scheme in the browser's settings.
If you have any suggestions, please comment in our openDesktop.org forums https://forum.opendesktop.org/ !