添加项目文件。

TagHelpers/ThemeToggleTagHelper.cs

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+using AcdiuTools.Services;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using System.Threading.Tasks;
+
+namespace AcdiuTools.TagHelpers
+{
+    /// <summary>
+    /// 主题切换按钮 Tag Helper
+    /// 用法: <theme-toggle />
+    /// </summary>
+    [HtmlTargetElement("theme-toggle")]
+    public class ThemeToggleTagHelper(IThemeService themeService) : TagHelper
+    {
+        private readonly IThemeService _themeService = themeService;
+
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            // 获取当前主题
+            var currentTheme = await _themeService.GetUserThemeAsync();
+            bool isDark = currentTheme == "dark";
+
+            // 设置标签名为 button
+            output.TagName = "button";
+            output.TagMode = TagMode.StartTagAndEndTag;
+
+            // 添加基础 CSS 类 (Bootstrap)
+            output.Attributes.Add("class", "btn btn-outline-secondary border-0");
+            output.Attributes.Add("id", "theme-toggle-btn");
+            output.Attributes.Add("type", "button");
+            output.Attributes.Add("aria-label", "Toggle Theme");
+
+            // 添加 Tooltip (Bootstrap data-bs-toggle)
+            output.Attributes.Add("data-bs-toggle", "tooltip");
+            output.Attributes.Add("data-bs-placement", "bottom");
+            output.Attributes.Add("title", isDark ? "切换到浅色模式" : "切换到深色模式");
+
+            // 根据当前主题设置图标内容
+            // 使用 Bootstrap Icons 或 FontAwesome
+            string iconHtml = isDark
+                ? "<i class=\"bi bi-sun-fill\"></i>" // 深色模式下显示太阳图标（暗示切换到亮）
+                : "<i class=\"bi bi-moon-stars-fill\"></i>"; // 浅色模式下显示月亮图标
+
+            output.Content.SetHtmlContent(iconHtml);
+        }
+    }
+}