fit: make a href style overridable

[EArminjon]

This PR make a tag style be overrided.

  "a": Style.fromTextStyle(
          const TextStyle(
            color: Colors.black,
            fontWeight: FontWeight.bold,
            decoration: TextDecoration.underline,
            decorationThickness: 4,
            decorationColor: Color(0xFFFCFC03),
          ),
        ),

Before :

After :

[Sub6Resources]

LGTM