Resolve "Courseware Akkordion bricht im Vollbildmodus um"

Closes #3759

Merge request studip/studip!2627

resources/assets/stylesheets/scss/courseware/containers/default-container.scss

@@ -6,7 +6,8 @@
         width: 100%;
     }
     &.cw-container-colspan-half {
-        max-width: 540px;
+        max-width: calc(50% - 5px);
+        min-width: 500px;
         width: 100%;
     }
     &.cw-container-colspan-half-center {
@@ -166,4 +167,4 @@ form.cw-container-dialog-edit-form {
             }
         }
     }
-}
+}
\ No newline at end of file