添加项目文件。

Services/IThemeService.cs

@@ -0,0 +1,26 @@
+using System.Threading.Tasks;
+
+namespace AcdiuTools.Services
+{
+    /// <summary>
+    /// 主题服务接口
+    /// 负责处理用户主题偏好的获取与持久化
+    /// </summary>
+    public interface IThemeService
+    {
+        /// <summary>
+        /// 获取当前用户的主题配置
+        /// 如果用户未登录或未设置，返回默认主题
+        /// </summary>
+        /// <returns>主题名称 (如 "light", "dark")</returns>
+        Task<string> GetUserThemeAsync();
+
+        /// <summary>
+        /// 保存用户的主题偏好
+        /// </summary>
+        /// <param name="userId">用户ID</param>
+        /// <param name="theme">主题名称</param>
+        /// <returns>是否保存成功</returns>
+        Task<bool> SaveUserThemeAsync(string userId, string theme);
+    }
+}

Services/ThemeService.cs

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+namespace AcdiuTools.Services
+{
+    /// <summary>
+    /// 主题服务实现
+    /// 使用 Cookie 作为持久化机制示例，实际项目中可替换为数据库
+    /// </summary>
+    public class ThemeService(IHttpContextAccessor httpContextAccessor) : IThemeService
+    {
+        private const string DefaultTheme = "light";
+        private const string ThemeCookieName = "UserThemePreference";
+        private readonly IHttpContextAccessor _httpContextAccessor = httpContextAccessor;
+
+        /// <summary>
+        /// 获取当前用户的主题配置
+        /// 优先级: Cookie > 默认值
+        /// </summary>
+        public Task<string> GetUserThemeAsync()
+        {
+            var context = _httpContextAccessor.HttpContext;
+            if (context != null && context.Request.Cookies.TryGetValue(ThemeCookieName, out var theme))
+            {
+                return Task.FromResult(theme);
+            }
+
+            // 这里可以扩展为查询数据库中的用户配置
+            return Task.FromResult(DefaultTheme);
+        }
+
+        /// <summary>
+        /// 保存用户的主题偏好到 Cookie
+        /// </summary>
+        public Task<bool> SaveUserThemeAsync(string userId, string theme)
+        {
+            var context = _httpContextAccessor.HttpContext;
+            if (context == null) return Task.FromResult(false);
+
+            var cookieOptions = new CookieOptions
+            {
+                Expires = DateTimeOffset.UtcNow.AddYears(1),
+                IsEssential = true,
+                HttpOnly = false, // 允许 JS 读取，以便前端立即应用样式
+                Secure = context.Request.IsHttps
+            };
+
+            context.Response.Cookies.Append(ThemeCookieName, theme, cookieOptions);
+
+            // 如果已登录，此处应同时更新数据库中的用户配置
+            // await _userRepository.UpdateThemeAsync(userId, theme);
+
+            return Task.FromResult(true);
+        }
+    }
+}