Fix default colours used by wxHtmlWindow in dark mode

Don't hardcode white background in wxHtmlWindow, but use
wxSYS_COLOUR_WINDOW, as was already done in wxHtmlWinParser in case when
wxHtmlWindow was not used at all.

Also use wxSYS_COLOUR_WINDOWTEXT for the default foreground and
light/dark-mode dependent link colour instead of hardcoded blue. As a
side effect, this uses a more appropriate colour for the links in the
light mode as well.

Add a link to the lists test page in the HTML test sample to allow
testing the links appearance easily (links present in the other pages of
this sample use fixed colours specified in HTML itself).

samples/html/test/listtest.htm

@@ -19,7 +19,7 @@
       <ul><li>List in a table, this cell should not wrap</li></ul>
     </td>
     <td>
-      Second column, unimportant
+      Click <a href="test.htm">here</a> to go to the initial page.
     </td>
   <tr>
 </table>

src/html/htmlwin.cpp

@@ -493,7 +493,7 @@ bool wxHtmlWindow::DoSetPage(const wxString& source)
     // ...and run the parser on it:
     wxClientDC dc(this);
     dc.SetMapMode(wxMM_TEXT);
-    SetBackgroundColour(wxColour(0xFF, 0xFF, 0xFF));
+    SetBackgroundColour(wxSystemSettings::GetColour(wxSYS_COLOUR_WINDOW));
     SetBackgroundImage(wxNullBitmap);
 
     double pixelScale = 1.0;

src/html/winpars.cpp

@@ -25,6 +25,7 @@
 #include "wx/fontmap.h"
 #include "wx/uri.h"
 
+#include "wx/private/hyperlink.h"
 
 //-----------------------------------------------------------------------------
 // wxHtmlWinParser
@@ -192,12 +193,11 @@ void wxHtmlWinParser::InitParser(const wxString& source)
 
     m_UseLink = false;
     m_Link = wxHtmlLinkInfo( wxEmptyString );
-    m_LinkColor.Set(0, 0, 0xFF);
-    m_ActualColor.Set(0, 0, 0);
-    const wxColour windowColour = wxSystemSettings::GetColour(wxSYS_COLOUR_WINDOW) ;
+    m_LinkColor = wxPrivate::GetLinkColour();
+    m_ActualColor = wxSystemSettings::GetColour(wxSYS_COLOUR_WINDOWTEXT);
     m_ActualBackgroundColor = m_windowInterface
                             ? m_windowInterface->GetHTMLBackgroundColour()
-                            : windowColour;
+                            : wxSystemSettings::GetColour(wxSYS_COLOUR_WINDOW);
     m_ActualBackgroundMode = wxBRUSHSTYLE_TRANSPARENT;
     m_Align = wxHTML_ALIGN_LEFT;
     m_ScriptMode = wxHTML_SCRIPT_NORMAL;