Specify controlbox size for lg breakpoint

css/converse.css

@@ -7724,6 +7724,10 @@ body.reset {
     #conversejs.converse-fullscreen .chatbox {
       flex: 0 0 75%;
       max-width: 75%; } }
+  @media (min-width: 992px) {
+    #conversejs.converse-fullscreen .chatbox {
+      flex: 0 0 75%;
+      max-width: 75%; } }
   @media (min-width: 1200px) {
     #conversejs.converse-fullscreen .chatbox {
       flex: 0 0 83.3333333333%;
@@ -8104,6 +8108,11 @@ body.reset {
     #conversejs.converse-mobile #controlbox {
       flex: 0 0 25%;
       max-width: 25%; } }
+  @media (min-width: 992px) {
+    #conversejs.converse-fullscreen #controlbox,
+    #conversejs.converse-mobile #controlbox {
+      flex: 0 0 25%;
+      max-width: 25%; } }
   @media (min-width: 1200px) {
     #conversejs.converse-fullscreen #controlbox,
     #conversejs.converse-mobile #controlbox {

sass/_chatbox.scss

@@ -579,6 +579,9 @@
         @include media-breakpoint-up(md) {
             @include make-col(9);
         }
+        @include media-breakpoint-up(lg) {
+            @include make-col(9);
+        }
         @include media-breakpoint-up(xl) {
             @include make-col(10);
         }

sass/_controlbox.scss

@@ -452,6 +452,9 @@
         @include media-breakpoint-up(md) {
             @include make-col(3);
         }
+        @include media-breakpoint-up(lg) {
+            @include make-col(3);
+        }
         @include media-breakpoint-up(xl) {
             @include make-col(2);
         }