change background color of code editor

File | Settings (Preferences for Mac OS) | Editor | Colors and Fonts | General | Default Text -> Background (you might need to "Save as" the default scheme before that), then choose the background color.

The Project Files area color is defined in IDE theme (Preferences/Appearance & Behavior/Appearance/Theme).
There are several ways to change it:
- 'Color Ide' plugin (https://plugins.jetbrains.com/plugin/7055?pr=webstorm)
- assigning background color to certain file groups: Preferences/Appearance & Behavior/File Colors, press Add, choose the desired color and  scope, make sure to enable 'Enable file colors' and 'Use in project  view'.
- creating your own IDE theme.  IDE Themes are java Look&Feels. It's technically possible to  install any third-party L&F into JVM and use it in WebStorm ( see https://weblogs.java.net/blog/kirillcool/archive/2005/08/intellij_idea_5.html for instructions), but it will most likely look ugly and break the UI in many places.

Thanks, it helped, but only parted. Background color of code editor works only for blocks before <?php tab and after ?> tags. Within this block background color is still white.
Which items have I to alter apart from "Default Text" ?

Now in my editor blocks of HTML and php are in white background like :
http://s017.radikal.ru/i432/1503/d7/f4c3bd008674.png

I want to show all background in gray.
I tried to search in settings, but failed.

Please change the 'Background' option of Preferences | Editor | Colors and Fonts | Language Defaults, Markup Tag accordingly

Thanks, it help for html tags!
Also I added backgroud color in some more places I need, but I did not find how to set color in in current line and in php-variables:
http://s017.radikal.ru/i405/1503/bc/790fdbf106be.png

Current line color:
Preferences | Editor | Colors and Fonts |General, Caret row.
PHP variable has a cdefault background - the one chosen for default text. Variable on your screenshot seems to be highlighted because some warning is being shown for it

Preferences | Editor | Colors Scheme | General | Text | Default text | Background