Add back support for Arc, Arc-Darker and Arc-Dark themes

data/media/css/gtk_arc.css

@@ -0,0 +1,5 @@
+@define-color foreground_color #3b3e45;
+@define-color background_color #f5f6f7;
+@define-color math_text_color #00364c;
+
+@import url("_gtk_base.css");

data/media/css/gtk_arc_dark.css

@@ -0,0 +1,5 @@
+@define-color foreground_color #d3dae3;
+@define-color background_color #383c4a;
+@define-color math_text_color #ffc9b3;
+
+@import url("_gtk_base.css");

data/media/css/gtk_arc_darker.css

@@ -0,0 +1,5 @@
+@define-color foreground_color #3b3e45;
+@define-color background_color #f5f6f7;
+@define-color math_text_color #00364C;
+
+@import url("_gtk_base.css");

data/media/css/web_arc.css

@@ -0,0 +1,18 @@
+@import url("_web_base.css");
+
+:root {
+  --text-color: #3b3e45;
+  --background-color: #f5f6f7;
+  --alt-background-color: #eceff2;
+  --link-color: #1a7bed;
+  --blockquote-text-color: #818894;
+  --blockquote-border-color: #d5d9dd;
+  --header-border-color: #e0e3e7;
+  --hr-background-color: #d7dbe0;
+  --table-tr-border-color: #bcc2c9;
+  --table-td-border-color: #d5d9dd;
+  --kbd-text-color: #5b626d;
+  --kbd-background-color: #f0f2f4;
+  --kbd-border-color: #bcc2c9;
+  --kbd-shadow-color: #8b949d;
+}

data/media/css/web_arc_dark.css

@@ -0,0 +1,18 @@
+@import url("_web_base.css");
+
+:root {
+  --text-color: #d3dae3;
+  --background-color: #383c4a;
+  --alt-background-color: #3d414f;
+  --link-color: #9ac6ff;
+  --blockquote-text-color: #8d949d;
+  --blockquote-border-color: #555967;
+  --header-border-color: #4a4e5c;
+  --hr-background-color: #535765;
+  --table-tr-border-color: #6c707e;
+  --table-td-border-color: #555967;
+  --kbd-text-color: #b3bac3;
+  --kbd-background-color: #3f4351;
+  --kbd-border-color: #6c707e;
+  --kbd-shadow-color: #9a9eac;
+}

data/media/css/web_arc_darker.css

@@ -0,0 +1 @@
+@import url("web_arc.css");

uberwriter/Theme.py

@@ -46,4 +46,11 @@ defaultThemes = [
           get_css_path('web_adwaita.css'), False, 'Adwaita-dark'),
     Theme('Adwaita-dark', get_css_path('gtk_adwaita_dark.css'),
           get_css_path('web_adwaita_dark.css'), True, 'Adwaita'),
+    # https://github.com/NicoHood/arc-theme/tree/master/common/gtk-3.0/3.20/sass
+    Theme('Arc', get_css_path('gtk_arc.css'),
+          get_css_path('web_arc.css'), False, 'Arc-Dark'),
+    Theme('Arc-Darker', get_css_path('gtk_arc_darker.css'),
+          get_css_path('web_arc_darker.css'), False, 'Arc-Dark'),
+    Theme('Arc-Dark', get_css_path('gtk_arc_dark.css'),
+          get_css_path('web_arc_dark.css'), True, 'Arc'),
 ]