Custom CSS classes

If you are using Bootstrap for DotVVM and you need to modify which css classes (classes on outer control element or classes on inner control structure) are used on Bootstrap 4 controls, than you can use bootstrap Custom CSS API to do so.

Basic usage

For example, let's say that you want to redefine <bs:ModalDialog ... /> body to also use css class custom-body instead of standard modal-body.

  1. Create derived class from ModalDialogCss with overridden ModalDialogBody property.
public class CustomModalDialogCss : ModalDialogCss
    public override string ModalDialogBody => "custom-body";
  1. Create derived class from BootstrapCss with overridden ModalDialog property.
public class CustomBootstrapCss : BootstrapCss
    public override IModalDialogCss ModalDialog => new CustomModalDialogCss();
  1. Register your CustomBootstrapCss class in DotvvmStartup.
config.Styles.Register<ModalDialog>().RegisterBootstrapCss(new CustomBootstrapCss(),dotvvmConfig);

Now every modal dialog would have custom-body css class instead of default modal-body. Because we have derived our classes from default implementations than all other classes would be the same.

We also could provide custom CSS for everything by implementing IBootstrapCss interface for our css classes aggregate and IControlNameCss (IModalDialogCss , ... ) for each control.

If we would want to register such custom css for all types of controls, than the registration would look like this:

config.Styles.RegisterBootstrapCss(new CustomBootstrapCss(), dotvvmConfig);

Restricting where would our custom CSS be used

If you don't wont our custom classes to be applied to every control, than we can restrict on which controls and under which conditions it would be used by Server-side Styles API.

For example if we want to limit our custom classes to only modal dialogs in admin section (has view in folder ~/Views/admin/) than we can register our CustomBootstrapCss this way:

config.Styles.Register<ModalDialog>().WithCondition(context => context.HasViewInDirectory("~/Views/admin/")).RegisterBootstrapCss(new CustomBootstrapCss(), dotvvmConfig);

Optional settings of Bootstrap Custom CSS

Behavior of Bootstrap Custom CSS can be further customized by setting some properties in DotvvmBootstrapOptions.


When set to true (it's true by default), than all control which does not have IBootstrapCss set will try to find some IBootstrapCss instance on their ancestors. If no instance is found, than the DefaultBootstrapCustomCss is used.

When set to false than no inheritance is performed. The control used explicitly set instance of IBootstrapCss or DefaultBootstrapCustomCss.


Instance of IBootstrapCss which will be used when no other css class is specified for control AND if InheritCustomCssFromParentControl is set to false.

If InheritCustomCssFromParentControl is true than Bootstrap custom CSS class from nearest ancestor with would be used.

If no custom css is found on any of the ancestors than DefaultBootstrapCustomCss is used.