[polari] Stop using Gtk.STYLE_CLASS_* constants

[Florian Müllner <fmuellner src gnome org>]

commit 2310e2bc2d93a63d3c9505aba66af16ab9255960
Author: Florian Müllner <fmuellner gnome org>
Date:   Sat Sep 26 02:24:12 2020 +0200

    Stop using Gtk.STYLE_CLASS_* constants
    
    They are gone in GTK4, so replace them with the corresponding
    style classes.
    
    https://gitlab.gnome.org/GNOME/polari/-/merge_requests/174

 src/initialSetup.js | 4 ++--
 src/urlPreview.js   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/src/initialSetup.js b/src/initialSetup.js
index 82831a00..b46cfdc1 100644
--- a/src/initialSetup.js
+++ b/src/initialSetup.js
@@ -88,9 +88,9 @@ var InitialSetupWindow = GObject.registerClass({
 
         let context = this._nextButton.get_style_context();
         if (isLastPage)
-            context.add_class(Gtk.STYLE_CLASS_SUGGESTED_ACTION);
+            context.add_class('suggested-action');
         else
-            context.remove_class(Gtk.STYLE_CLASS_SUGGESTED_ACTION);
+            context.remove_class('suggested-action');
 
         this._nextButton.grab_default();
         this._updateNextSensitivity();
diff --git a/src/urlPreview.js b/src/urlPreview.js
index 44fef4a3..33b7a24e 100644
--- a/src/urlPreview.js
+++ b/src/urlPreview.js
@@ -113,7 +113,7 @@ var URLPreview = GObject.registerClass({
 
         let styleContext = this.get_style_context();
         styleContext.add_class('url-preview');
-        styleContext.add_class(Gtk.STYLE_CLASS_BACKGROUND);
+        styleContext.add_class('background');
 
         this._imageLoaded = false;
         this._image = new Gtk.Image({
@@ -127,7 +127,7 @@ var URLPreview = GObject.registerClass({
             ellipsize: Pango.EllipsizeMode.END,
             visible: true,
         });
-        this._label.get_style_context().add_class(Gtk.STYLE_CLASS_DIM_LABEL);
+        this._label.get_style_context().add_class('dim-label');
         this.add(this._label);
 
         this._networkMonitor = Gio.NetworkMonitor.get_default();