fix contents width for preview

src/client/styles/scss/_on-edit.scss

@@ -243,11 +243,6 @@ body.on-edit {
       overflow-y: scroll;
     }
 
-    .wiki {
-      max-width: 980px;
-      margin: 0 auto;
-    }
-
     .grw-editor-configuration-dropdown {
       .icon-container {
         width: 20px;
@@ -304,6 +299,20 @@ body.on-edit {
   }
 }
 
+body.on-edit {
+  &:not(.growi-layout-fluid) .page-editor-preview-body {
+    .wiki {
+      max-width: 980px;
+      margin: 0 auto;
+    }
+  }
+  &.growi-layout-fluid .page-editor-preview-body {
+    .wiki {
+      margin: 0 auto;
+    }
+  }
+}
+
 // overwrite .CodeMirror pre
 .CodeMirror pre.CodeMirror-line {
   font-family: $font-family-monospace;