Add support for HighContrast and HighContrastInverse themes

data/media/css/gtk_high_contrast.css

@@ -0,0 +1,5 @@
+@define-color foreground_color #000000;
+@define-color background_color #ffffff;
+@define-color math_text_color #000000;
+
+@import url("_gtk_base.css");

data/media/css/gtk_high_contrast_inverse.css

@@ -0,0 +1,5 @@
+@define-color foreground_color #ffffff;
+@define-color background_color #000000;
+@define-color math_text_color #ffffff;
+
+@import url("_gtk_base.css");

data/media/css/web_high_contrast.css

@@ -0,0 +1,26 @@
+@import url("_web_base.css");
+
+a {
+  text-decoration: underline;
+}
+
+pre {
+  border: 1px solid;
+}
+
+:root {
+  --text-color: #000000;
+  --background-color: #ffffff;
+  --alt-background-color: #ffffff;
+  --link-color: #000000;
+  --blockquote-text-color: #000000;
+  --blockquote-border-color: #000000;
+  --header-border-color: #000000;
+  --hr-background-color: #000000;
+  --table-tr-border-color: #000000;
+  --table-td-border-color: #000000;
+  --kbd-text-color: #000000;
+  --kbd-background-color: #ffffff;
+  --kbd-border-color: #000000;
+  --kbd-shadow-color: #000000;
+}

data/media/css/web_high_contrast_inverse.css

@@ -0,0 +1,26 @@
+@import url("_web_base.css");
+
+a {
+  text-decoration: underline;
+}
+
+pre {
+  border: 1px solid;
+}
+
+:root {
+  --text-color: #ffffff;
+  --background-color: #000000;
+  --alt-background-color: #000000;
+  --link-color: #ffffff;
+  --blockquote-text-color: #ffffff;
+  --blockquote-border-color: #ffffff;
+  --header-border-color: #ffffff;
+  --hr-background-color: #ffffff;
+  --table-tr-border-color: #ffffff;
+  --table-td-border-color: #ffffff;
+  --kbd-text-color: #ffffff;
+  --kbd-background-color: #000000;
+  --kbd-border-color: #ffffff;
+  --kbd-shadow-color: #ffffff;
+}

uberwriter/Theme.py

@@ -53,4 +53,9 @@ defaultThemes = [
           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'),
+    # https://gitlab.gnome.org/GNOME/gtk/tree/master/gtk/theme/HighContrast
+    Theme('HighContrast', get_css_path('gtk_high_contrast.css'),
+          get_css_path('web_high_contrast.css'), False, 'HighContrastInverse'),
+    Theme('HighContrastInverse', get_css_path('gtk_high_contrast_inverse.css'),
+          get_css_path('web_high_contrast_inverse.css'), True, 'HighContrast'),
 ]