How to create a theme option for controls in windows form in C#

Here's a rough "skeleton" of what the beginnings of a style manager for WinForms might look like:

public static class VisualStyleManager
{
   public static Dictionary<string, VisualStyle> StyleDictionary { set; get; }

   public static void AddStyle(string name, Control control)
   {
        StyleDictionary.Add(name, new VisualStyle(control));
   }
 
   public static void ApplyStyle(string stylename, Control control)
   {
       VisualStyle style;

       if(StyleDictionary.TryGetValue(stylename, out vs)
       {
           control.BackColor = vs.BackColor;
           control ForeColor = vs.ForeColor;
           control.Font = vs.Font;
       }     
   }
}

public class VisualStyle
{
    public Color CBackColor { set; get; }
    public Color CForeColor { set; get; }

    public Font CFont {set; get; }

    public VisualStyle(Control control)
    {
        CBackColor = control.BackColor;
        CForeColor = control.ForeColor;
        CFont = control.Font;
    }
}

Here's how it might be used:

private void SetAllFormButtons(Form form, button abutton)
{
   VisualStyleManager.AddStyle("ButtonStyle1", button1);

   foreach (var btn in this.GetControlsByType<Button>())
   {
       if (btn != button1)
       {
           VisualStyleManager.ApplyStyle("ButtonStyle1", btn);
       }
   }
}

This makes use of an extension Method:

public static class ControlExtensions
{
    public static IEnumerable<Control> GetControlsByType<T>(this Control control)
    {
        Stack<Control> stack = new Stack<Control>();

        stack.Push(control);

        while (stack.Any())
        {
            Control nextcontrol = stack.Pop();

            foreach (Control childControl in nextcontrol.Controls)
            {
                stack.Push(childControl);
            }

            if (nextcontrol is T) yield return nextcontrol;
        }
    }
}

Now consider what you are going to have to deal with to make this handle WinForm Control Properties like a Form's 'FormBorderStyle, or a Button's FlatStyle, and FlatAppearance Properties; these Properties are not exposed when you cast these Controls to their Control base Type.

For every unique Control Type's Property, you will have to handle that as a special case. However, there are other ways, making heavy use of 'Reflection, to do this. And, you can take the "skeleton" here and sub-class VisualStyle to handle other Control Types with "special requirements."

By now, you may have figured out that to get anything substantial going with theming involves (probably) a lot of work on your part. While doing this may improve your design skills and knowledge of WinForms internals, if you are at a relatively early phase in studying and using WinForms and C#, I suggest you do not take on trying to write a full-featured theme facility.

There are other strategies you could pursue: such as, displaying a Property Browser at run-time to let the user edit colors, fonts, etc. Let's say User1 edited the BackColor of any one Button; you could get a notification of that event and then set all the other Buttons to use that same BackColor.