shrink message dialog titlebars

common/gtk-3.0/3.20/gtk-dark.css

@@ -2451,6 +2451,7 @@ calendar {
     color: #D3DAE3; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: rgba(47, 52, 63, 0.97);
   border-bottom: 1px solid rgba(32, 35, 43, 0.97); }
 

common/gtk-3.0/3.20/gtk-darker.css

@@ -2450,6 +2450,7 @@ calendar {
     color: #5c616c; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: rgba(47, 52, 63, 0.97);
   border-bottom: 1px solid rgba(32, 35, 43, 0.97); }
 

common/gtk-3.0/3.20/gtk-solid-dark.css

@@ -2451,6 +2451,7 @@ calendar {
     color: #D3DAE3; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: #2f343f;
   border-bottom: 1px solid #20232b; }
 

common/gtk-3.0/3.20/gtk-solid-darker.css

@@ -2450,6 +2450,7 @@ calendar {
     color: #5c616c; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: #2f343f;
   border-bottom: 1px solid #20232b; }
 

common/gtk-3.0/3.20/gtk-solid.css

@@ -2454,6 +2454,7 @@ calendar {
     color: #5c616c; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: #e7e8eb;
   border-bottom: 1px solid #d4d5db; }
 

common/gtk-3.0/3.20/gtk.css

@@ -2454,6 +2454,7 @@ calendar {
     color: #5c616c; }
 
 messagedialog .titlebar {
+  min-height: 20px;
   background-color: rgba(231, 232, 235, 0.95);
   border-bottom: 1px solid rgba(212, 213, 219, 0.95); }
 

common/gtk-3.0/3.20/sass/_common.scss

@@ -2479,7 +2479,11 @@ calendar {
 //
 messagedialog { // Message Dialog styling
 
-  .titlebar { background-color: $header_bg; border-bottom: 1px solid darken($header_bg, 7%) }
+  .titlebar {
+    min-height: 20px;
+    background-color: $header_bg;
+    border-bottom: 1px solid darken($header_bg, 7%);
+  }
 
   .dialog-action-area button { padding: 8px; min-height: 0; }