ant-design-blazor/site/AntDesign.Docs/Shared/FixedWidgets.razor.cs

using System.Threading.Tasks;
using AntDesign.Docs.Localization;
using Microsoft.AspNetCore.Components;
using Microsoft.JSInterop;
using System.Collections.Generic;

namespace AntDesign.Docs.Shared
{
    public partial class FixedWidgets
    {
        [Inject] private ILanguageService Language { get; set; }
        [Inject] private IJSRuntime JS { get; set; }

        private ElementReference _linkRef;

        private string _themeFileUrl;


        private async Task ChangeTheme(string theme)
        {
            _themeFileUrl = $"_content/AntDesign.Docs/css/docs.{theme}.css";

            await JS.InvokeVoidAsync(JSInteropConstants.SetDomAttribute, "body", new Dictionary<string, string>
            {
                ["data-theme"] = theme
            });

            await JS.InvokeVoidAsync(JSInteropConstants.AddElementToBody, _linkRef);
        }
    }
}