Normally (in HTML/XML file) that would be Tag
style. And XML styles may be taking over HTML here (as an underlying language in IDE's styling hierarchy perhaps).
I'm not sure if this will work here but try this anyway (can be used in other scenarios):
Help | Find Action...
(or Search Everywhere and focus on "Actions" tab)Jump to Colors and Fonts
entry there and invoke it.P.S. It's not a "text shadow" but a background color.