css: select by id only

This allows us to support all GTK versions.

src/iridium.css

@@ -1,16 +1,16 @@
-GtkSourceView#source-view {
+#source-view {
   font-family: "Fira Mono", monospace;
   font-size: 1.05em;
 }
 
-GtkEntry#title-entry {
+#title-entry {
   border: none;
   background: none;
   font-size: x-large;
   font-weight: bold;
 }
 
-GtkPaned#main-pane {
+#main-pane {
   background: white;
   border: 1px solid #ccc;
 }
@@ -19,6 +19,6 @@ GtkPaned#main-pane {
   border-bottom: 1px solid #ccc;
 }
 
-GtkBox#tags GtkLabel {
+#tags GtkLabel {
   color: #aaa;
 }