How to delete design configuration?
There is no provision to delete these from admin panel.
The screenshot you shared is loaded from
design_config_grid_flat table. You can delete entries from there.
If you wanna delete any theme then follow the steps.
STEP 1 : Goto
theme table and delete the entry for your created theme, remember the deleted
STEP 2 : Now goto
core_config_data table and look for path design/theme/theme_id using your deleted
theme_id. Remove it as well.
Run the following commands.
php bin/magento cache:flush php bin/magento indexer:reindex
Hope this is helpful.