Please address the comments from this code review:

## Overall Comments
- Consider moving the inline styles for the wrapper and backdrop in `UniverSheet.razor` into CSS classes so layout and visual behavior are centralized and easier to maintain or override.
- When defaulting `LoadingText` with `Localizer[nameof(LoadingText)]`, consider adding a fallback (e.g., to a hard-coded string) so the UI doesn’t show the resource key if a corresponding localization entry is missing.

## Individual Comments

### Comment 1
<location> `src/components/BootstrapBlazor.UniverSheet/wwwroot/univer.js:117-119` </location>
<code_context>
         univerAPI.createWorkbook();
     }

+    const { onRendered } = sheet.events;
+    if (onRendered) {
+        const disposable = univerAPI.addEvent(univerAPI.Event.LifeCycleChanged, e => {
+            const { stage } = e;
+            if (stage === univerAPI.Enum.LifecycleStages.Rendered) {
</code_context>

<issue_to_address>
**issue (bug_risk):** Guard against `sheet.events` being undefined before destructuring.

If callers omit `sheet.events`, `const { onRendered } = sheet.events;` will throw at runtime. Consider using optional chaining (e.g. `const onRendered = sheet.events?.onRendered;`) or ensuring `sheet.events` is defaulted when constructing `sheet` to handle partial/legacy callers safely.
</issue_to_address>

### Comment 2
<location> `src/components/BootstrapBlazor.UniverSheet/Components/UniverSheet.razor:5-7` </location>
<code_context>
 @attribute [JSModuleAutoLoader("./_content/BootstrapBlazor.UniverSheet/Components/UniverSheet.razor.js", JSObjectReference = true)]

-<div @attributes="@AdditionalAttributes" class="@ClassString" id="@Id"></div>
+<div @attributes="@AdditionalAttributes" class="@ClassString" id="@Id" style="position: relative; overflow: hidden;">
+    <div class="bb-univer-sheet-wrap" style="height: 100%;"></div>
+    <div class="bb-univer-sheet-backdrop" style="background-color: #000; opacity: 0.3; position: absolute; inset: 0; z-index: 1205; display: flex; align-items: center; justify-content: center;">
+        <div style="color: #fff;">@LoadingText</div>
+    </div>
</code_context>

<issue_to_address>
**suggestion:** Consider moving inline styles to CSS to keep layout/styling consistent and maintainable.

These elements now depend on complex inline styles for positioning and centering. Moving these into CSS classes (e.g., extending `.bb-univer-sheet` and defining `.bb-univer-sheet-backdrop`) will simplify future layout/theming changes and prevent clashes with user inline styles from `AdditionalAttributes`.

Suggested implementation:

```
<div @attributes="@AdditionalAttributes" class="@($"{ClassString} bb-univer-sheet")" id="@Id">
    <div class="bb-univer-sheet-wrap"></div>
    <div class="bb-univer-sheet-backdrop">
        <div class="bb-univer-sheet-loading-text">@LoadingText</div>
    </div>
</div>

```

To complete the refactor away from inline styles, add CSS for these classes in the appropriate stylesheet (e.g. `UniverSheet.razor.css`, the library's main `.css`, or a shared theme file):

```css
.bb-univer-sheet {
    position: relative;
    overflow: hidden;
}

.bb-univer-sheet-wrap {
    height: 100%;
}

.bb-univer-sheet-backdrop {
    background-color: #000;
    opacity: 0.3;
    position: absolute;
    inset: 0;
    z-index: 1205;
    display: flex;
    align-items: center;
    justify-content: center;
}

.bb-univer-sheet-loading-text {
    color: #fff;
}
```

If `ClassString` already includes `bb-univer-sheet`, adjust the `class` attribute to avoid duplication (e.g. via the existing class-composition helper used elsewhere in the codebase).
</issue_to_address>