uses IOUtils, Vcl.Styles, vcl.Themes;

procedure TForm1.FormCreate(Sender: TObject);
var
  dir, fileName, styleName: string;
begin
  //VCL 的样式文件 *.vsf 在 X:\Program Files\Embarcadero\RAD Studio\9.0\Redist\styles\vcl\
  dir := GetEnvironmentVariable('Delphi') + '\Redist\styles\vcl';

  {载入所有 *.vsf 文件}
  for fileName in TDirectory.GetFiles(dir, '*.vsf') do
    TStyleManager.LoadFromFile(fileName);

  {将样式名称导入列表}  
  for styleName in TStyleManager.StyleNames do
    ListBox1.Items.Add(styleName);
end;

{修改样式}
procedure TForm1.ListBox1Click(Sender: TObject);
begin
  TStyleManager.SetStyle(ListBox1.Items[ListBox1.ItemIndex]);
end;