MAGETWO-75311: #10510 - fix RWD with installed Sample Data #10929

Author: vrann

app/design/frontend/Magento/blank/web/css/source/_layout.less

@@ -21,6 +21,7 @@
             .lib-vendor-prefix-flex-basis(100%);
             .lib-vendor-prefix-flex-grow(1);
             .lib-vendor-prefix-order(1);
+            width: 100%; 
         }
 
         .sidebar-main {