Add Postbox message authoring and concurrency

webui/src/styles/postbox.css

@@ -518,6 +518,31 @@
   color: var(--muted);
 }
 
+.postbox-message-dialog {
+  width: min(720px, calc(100vw - 32px));
+}
+
+.postbox-compose-grid {
+  display: grid;
+  grid-template-columns: minmax(0, 2fr) minmax(160px, 1fr);
+  gap: 12px;
+}
+
+.postbox-compose-wide {
+  grid-column: 1 / -1;
+}
+
+.postbox-compose-grid textarea {
+  width: 100%;
+  min-height: 180px;
+  resize: vertical;
+}
+
+.postbox-dialog-actions.end {
+  justify-content: flex-end;
+  gap: 8px;
+}
+
 .postbox-admin-page > .segmented-control {
   margin-bottom: 14px;
 }
@@ -667,4 +692,8 @@
     align-items: flex-start;
     flex-direction: column;
   }
+
+  .postbox-compose-grid {
+    grid-template-columns: 1fr;
+  }
 }