Basic no-wallpaper support

src/components/settings_modal/tabs/general_tab.js

@@ -34,6 +34,10 @@ const GeneralTab = {
       return this.$store.state.instance.postFormats || []
     },
     instanceSpecificPanelPresent () { return this.$store.state.instance.showInstanceSpecificPanel },
+    instanceWallpaperUsed () {
+      return this.$store.state.instance.background &&
+        !this.$store.state.users.currentUser.background_image
+    },
     ...SharedComputedObject()
   }
 }

src/components/settings_modal/tabs/general_tab.vue

@@ -11,6 +11,11 @@
             {{ $t('settings.hide_isp') }}
           </Checkbox>
         </li>
+        <li v-if="instanceWallpaperUsed">
+          <Checkbox v-model="hideInstanceWallpaper">
+            {{ $t('settings.hide_wallpaper') }}
+          </Checkbox>
+        </li>
       </ul>
     </div>
     <div class="setting-item">

src/components/settings_modal/tabs/theme_tab/theme_tab.scss

@@ -165,7 +165,8 @@
     border-color: var(--border, $fallback--border);
     margin: 1em 0;
     padding: 1em;
-    background: var(--body-background-image);
+    background-color: var(--wallpaper);
+    background-image: var(--body-background-image);
     background-size: cover;
     background-position: 50% 50%;