The default theme is part of simple machines forum installation which contains the base templates and language files that will make the forum display correctly. Modifying the default theme or deleting files that are part of it will make it difficult to upgrade, install, modify, or add more themes in the future. It is recommended to keep the default theme in one piece, and if a file is corrupted or missing from another theme simple machines forum will have the option to fall back to the default theme.

If it is desired to make changes to the forum the best way is to make a copy of the original default theme and modify it. In that matter if something is incorrect, or missing in the modified theme the forum will not be affected in any way. The reason is modified themes often use templates or language files that the default theme has, and if a template or a language file is missing or corrupted simple machines will look for the templates in the theme that is based on.

In that matter simple machines forum will load them from the default theme. Keep in mind that images and stylesheet from the default theme are not part of the fall back system. The purpose of the fall back system is to make the theme development more simple. If it is the desire to develop themes please refer to Creating and Understanding Themes in the online manual.