RenderFragment GetButton(this ComponentBase caller, ButtonType buttonType, Theme buttonTheme)
{
    return (builder) =>
    {

    };
}

@this.GetButton(ButtonType.Icon, Theme.Primary)

public static class ComponentExtension
{
    //user must supply all parameters except optional ones which are optional
    //Extension component name must start with a Get and returns RenderFragment
    //Can have parameters and even optional ones
	
	//this component can be used from any component
    public static RenderFragment GetButton(this ComponentBase callerComponent, ButtonType buttonType, Theme buttonTheme, EventCallback click, int optionalParameter = 0)
    {
        return @<button @onclick="click" class="@buttonType @buttonTheme"></button>;
    }

	//this component can be used from any component
    public static RenderFragment GetButton2(this ComponentBase callerComponent, ButtonType buttonType, Theme buttonTheme, EventCallback click, int optionalParameter = 0)
    {
        return (builder) => 
        {
             builder.OpenElement("button");
             //more builders
             builder.CloseElement();
        }
    }
	
	//this component can be used only in CardComponent or super classes
	public static RenderFragment GetButton3(this CardComponent callerComponent, ButtonType buttonType, Theme buttonTheme, EventCallback click, int optionalParameter = 0)
    {
        return (builder) => 
        {
             builder.OpenElement("button");
             //more builders
             builder.CloseElement();
        }
    }
	
	//this component can be used only in super classes of MyBaseComponent
	public static RenderFragment GetButton4<TComponent>(this CardComponent callerComponent, ButtonType buttonType, Theme buttonTheme, EventCallback click, int optionalParameter = 0) where TComponent : MyBaseComponent
    {
        return (builder) => 
        {
             builder.OpenElement("button");
             //more builders
             builder.CloseElement();
        }
    }
}

<Button ButtonType="ButtonType.Icon" ButtonTheme="Theme.Primary" Click="DoSomething"></Button>
<Button2 ButtonType="ButtonType.Icon" ButtonTheme="Theme.Primary" Click="DoSomething"></Button2>

builder.AddContent(1, this.GetButton(ButtonTyp.Icon, Theme.Primary, EventCallback.Factory.Create(this, DoSomething)));