send: update layout on mobile

On mobile the keyboard covered half of the buttons, changed form
to be aligned at the top of the screen and made textarea a bit
smaller so that the mobile keyboard and the form are both visible.

src/form.css

@@ -76,6 +76,14 @@ textarea:focus {
 #newMessage textarea:focus {
   min-height: 18rem;
 }
+@media (orientation: portrait) {
+  #newMessage textarea {
+    min-height: 8rem;
+  }
+  #newMessage textarea:focus {
+    min-height: 15rem;
+  }
+}
 
 .buttons {
   align-items: center;

src/write.css

@@ -24,6 +24,11 @@
   width: 100vw;
   z-index: 20;
 }
+@media (orientation: portrait) {
+  #newMessage {
+    align-items: start;
+  }
+}
 
 #newMessage #writeForm {
   align-items: start;