gtk: use predifined css classes instead of custom ones

resources/client_row.ui

@@ -66,6 +66,7 @@
 						<property name="valign">center</property>
 						<property name="halign">center</property>
 						<property name="name">delete-button</property>
+						<style><class name="error"/></style>
 					</object>
 				</child>
 			</object>

resources/resources.gresource.xml

@@ -3,8 +3,6 @@
   <gresource prefix="/de/feschber/LanMouse">
     <file compressed="true" preprocess="xml-stripblanks">window.ui</file>
     <file compressed="true" preprocess="xml-stripblanks">client_row.ui</file>
-    <file compressed="true">style.css</file>
-    <file compressed="true">style-dark.css</file>
   </gresource>
   <gresource prefix="/de/feschber/LanMouse/icons">
 	<file compressed="true" preprocess="xml-stripblanks">de.feschber.LanMouse.svg</file>

resources/style-dark.css

@@ -1,11 +0,0 @@
-#delete-button {
-  color: @red_1;
-}
-
-#port-edit-cancel {
-  color: @red_1;
-}
-
-#port-edit-apply {
-  color: @green_1;
-}

resources/style.css

@@ -1,11 +0,0 @@
-#delete-button {
-  color: @red_3;
-}
-
-#port-edit-cancel {
-  color: @red_3;
-}
-
-#port-edit-apply {
-  color: @green_3;
-}

resources/window.ui

@@ -84,6 +84,7 @@
 																<property name="valign">center</property>
 																<property name="visible">false</property>
 																<property name="name">port-edit-apply</property>
+																<style><class name="success"/></style>
 															</object>
 														</child>
 														<child>
@@ -93,6 +94,7 @@
 																<property name="valign">center</property>
 																<property name="visible">false</property>
 																<property name="name">port-edit-cancel</property>
+																<style><class name="error"/></style>
 															</object>
 														</child>
 													</object>

src/frontend/gtk.rs

@@ -12,7 +12,7 @@ use crate::frontend::gtk::window::Window;
 
 use adw::Application;
 use gtk::{
-    gdk::Display, glib::clone, prelude::*, subclass::prelude::ObjectSubclassIsExt, CssProvider,
+    gdk::Display, glib::clone, prelude::*, subclass::prelude::ObjectSubclassIsExt,
     IconTheme,
 };
 use gtk::{gio, glib, prelude::ApplicationExt};
@@ -51,23 +51,12 @@ fn gtk_main() -> glib::ExitCode {
         .build();
 
     app.connect_startup(|_| load_icons());
-    app.connect_startup(|_| load_css());
     app.connect_activate(build_ui);
 
     let args: Vec<&'static str> = vec![];
     app.run_with_args(&args)
 }
 
-fn load_css() {
-    let provider = CssProvider::new();
-    provider.load_from_resource("de/feschber/LanMouse/style.css");
-    gtk::style_context_add_provider_for_display(
-        &Display::default().expect("Could not connect to a display."),
-        &provider,
-        gtk::STYLE_PROVIDER_PRIORITY_APPLICATION,
-    );
-}
-
 fn load_icons() {
     let display = &Display::default().expect("Could not connect to a display.");
     let icon_theme = IconTheme::for_display(display);