[ui] fix centering in image viewer

webui/src/components/display/blobs/ImageViewer.svelte

@@ -28,23 +28,28 @@
   }
 </script>
 
-{#if !imageLoaded}
-  <Spinner centered />
-{/if}
-<img
-  class="preview-image"
-  src="api/thumb/{address}"
-  alt={address}
-  on:load={loaded}
-  bind:this={imageEl}
-  draggable="false"
-/>
+<div class="image-viewer">
+  {#if !imageLoaded}
+    <Spinner centered />
+  {/if}
+  <img
+    class="preview-image"
+    src="api/thumb/{address}"
+    alt={address}
+    on:load={loaded}
+    bind:this={imageEl}
+    draggable="false"
+  />
+</div>
 
 <style global lang="scss">
   @use "@recogito/annotorious/dist/annotorious.min.css";
 
-  .preview-image {
-    max-width: 100%;
+  .image-viewer {
+    text-align: center;
+    img {
+      max-width: 100%;
+    }
   }
 
   .r6o-tag {