I have applied this theme to WebStorm, but I do not like it.
How can I revert to WebStorm's default setting?
Depending on what OS you are on, you should be able to remove the config file and WebStorm will recreate it.
Normally, there are .idea
folders as @camden_kid said.
https://www.jetbrains.com/help/webstorm/2016.1/project-and-ide-settings.html
<User home>\.WebStormXX\config that contains user-specific settings.
<User home> in WindowsXP is C:\Documents and Settings\<User name>\;
in Windows Vista it is C:\Users\<User name>\
/.WebStormXX/config that contains user-specific settings
~/Library/Preferences/WebStormXX contains the rest of the configuration settings.
You might be able to just swap theme depending on how destructive the theme files were.