Fix spelling error in Gradients docs (#18572)

docs/designers-developers/developers/themes/theme-support.md

@@ -136,7 +136,7 @@ The class name is built appending 'has-', followed by the class name _using_ keb
 
 ### Block Gradient Presets
 
-Different blocks have the possibility of selecting from a list of predined of gradients. The block editor provides a default gradient presets, but a theme can overwrite them and provide its own:
+Different blocks have the possibility of selecting from a list of predefined gradients. The block editor provides a default gradient presets, but a theme can overwrite them and provide its own:
 
 ```php
 add_theme_support(