Maui Bootstrap Theme

MauiBootstrapTheme Styling Guide

Bootstrap 5 styling for .NET MAUI via CSS-generated ResourceDictionaries. NuGet: Plugin.Maui.BootstrapTheme.

Setup

1. Install NuGet

<PackageReference Include="Plugin.Maui.BootstrapTheme" />

2. Add CSS themes to .csproj

<ItemGroup>
  <BootstrapCss Include="Resources\Themes\bootstrap.min.css" ThemeName="default" />
  <BootstrapCss Include="Resources\Themes\darkly.min.css" />
</ItemGroup>

For MauiReactor projects, also enable Reactor code generation:

<PropertyGroup>
  <BootstrapThemeGenerateReactor>true</BootstrapThemeGenerateReactor>
</PropertyGroup>

This generates a Bs constants class and *ReactorTheme classes alongside the ResourceDictionaries.

Download CSS from Bootswatch or use stock Bootstrap 5.

3. Register in MauiProgram.cs

// XAML app:
builder.UseMauiApp<App>()
    .UseBootstrapTheme(options => {
        options.AddTheme<Themes.DefaultTheme>("default");
        options.AddTheme<Themes.DarklyTheme>("darkly");
    });

// MauiReactor app:
builder.UseMauiReactorApp<MainPage>()
    .UseBootstrapTheme(options => {
        options.AddTheme<Themes.DefaultTheme>("default");
    });

4. Load theme in App.xaml.cs

Resources.MergedDictionaries.Add(new Themes.DefaultTheme());
BootstrapTheme.SyncFromResources(Resources);

Theme classes (e.g., DefaultTheme) are auto-generated at build time into obj/BootstrapTheme/.

MauiReactor: Bs Constants Pattern

When BootstrapThemeGenerateReactor=true, the build generates:

• Bs static class — const string keys for all Bootstrap CSS classes + spacing constants
• *ReactorTheme classes — MauiReactor Theme subclasses with color properties and class-based style support

Rules for MauiReactor code:

• Typography (h1–h6, lead, small, text-muted) → use .Class(Bs.H1)
• Buttons, forms, cards, backgrounds → use .Class(Bs.BtnPrimary), compose with .Class(Bs.BtnPrimary).Class(Bs.BtnLg)
• Spacing → use Bs.Spacing0 through Bs.Spacing5 (0, 4, 8, 16, 24, 48 dp) and BsPadding0..5 / BsMargin0..5 helpers
• Never use raw strings — always use Bs.* constants for IntelliSense and typo prevention

// ✅ Correct MauiReactor patterns:
Label("Dashboard").Class(Bs.H1)
Button("Save").Class(Bs.BtnPrimary)
Button("Delete").Class(Bs.BtnDanger).Class(Bs.BtnSm)
Entry().Class(Bs.FormControl)
Border(content).Class(Bs.Card).Class(Bs.Shadow)
VStack(spacing: Bs.Spacing3, ...)
Border(content).BsPadding3()
Border(content).BsMargin2()

// ❌ Do NOT use raw strings:
Label("Dashboard").Class("h1")        // Use Bs constant
Button("Save").Class("btn-primary")   // Use Bs.BtnPrimary

Critical Rules

ALWAYS apply StyleClass to EVERY styled control. A bare <Button Text="Save"/> gets no Bootstrap styling. Write <Button Text="Save" StyleClass="btn-primary"/>.

ALWAYS use DynamicResource (not StaticResource) for color/theme keys — enables runtime theme switching.

ALWAYS set page background:

this.BackgroundColor = BootstrapTheme.Current.GetBackground();

StyleClass Reference

Buttons

Combine classes with comma: StyleClass="btn-primary,btn-lg" or StyleClass="btn-outline-danger,btn-sm"

Buttons include visual states: Pressed darkens bg, PointerOver lightens bg (desktop), Disabled = 0.65 opacity.

XAML

<Button Text="Save" StyleClass="btn-primary"/>
<Button Text="Delete" StyleClass="btn-outline-danger,btn-sm"/>
<Button Text="Submit" StyleClass="btn-success,btn-lg"/>
<Button Text="Disabled" StyleClass="btn-primary" IsEnabled="False"/>

C# / MauiReactor

// C#
new Button { Text = "Save", StyleClass = { "btn-primary" } };
// MauiReactor — use Bs constants for IntelliSense + type safety
Button("Save").Class(Bs.BtnPrimary)
Button("Delete").Class(Bs.BtnOutlineDanger).Class(Bs.BtnSm)

Typography (Label)

Text color classes:

Combine freely: StyleClass="h4,text-muted" or StyleClass="lead,text-primary"

XAML

<Label Text="Page Title" StyleClass="h1"/>
<Label Text="Subtitle" StyleClass="lead,text-muted"/>
<Label Text="Field Label" StyleClass="form-label"/>
<Label Text="On blue card" StyleClass="h5,on-primary"/>

C# / MauiReactor

// C#
new Label { Text = "Page Title", StyleClass = { "h1" } };
// MauiReactor — use Class() consistently for typography
Label("Page Title").Class(Bs.H1)
Label("Subtitle").Class(Bs.Lead)
Label("Field Label").Class(Bs.FormLabel)

Form Inputs

Every input control MUST have a StyleClass. A bare <Entry/> is unstyled.

XAML

<Label Text="Email" StyleClass="form-label"/>
<Entry Placeholder="name@example.com" StyleClass="form-control"/>

<Label Text="Message" StyleClass="form-label"/>
<Editor Placeholder="Type here..." StyleClass="form-control" HeightRequest="100"/>

<Label Text="Country" StyleClass="form-label"/>
<Picker Title="Select..." StyleClass="form-select"/>

<SearchBar Placeholder="Search..." StyleClass="form-control"/>
<DatePicker StyleClass="form-control"/>
<TimePicker StyleClass="form-control"/>

<CheckBox StyleClass="form-check-input"/>
<Label Text="Remember me" StyleClass="form-check-label"/>

<Switch StyleClass="form-switch"/>
<Slider StyleClass="form-range"/>

C# / MauiReactor

Label("Email").Class(Bs.FormLabel)
Entry().Placeholder("name@example.com").Class(Bs.FormControl)
Picker().Title("Select...").Class(Bs.FormSelect)
CheckBox().Class(Bs.FormCheckInput)
Switch().Class(Bs.FormSwitch)

Cards & Containers (Border)

XAML

<!-- Basic card -->
<Border StyleClass="card">
    <VerticalStackLayout>
        <Label Text="Card Title" StyleClass="h5"/>
        <Label Text="Card content" StyleClass="text-muted"/>
    </VerticalStackLayout>
</Border>

<!-- Card with shadow and hover effect -->
<Border StyleClass="card,shadow,card-hoverable">
    <VerticalStackLayout>
        <Label Text="Hover me" StyleClass="h5"/>
        <Button Text="Action" StyleClass="btn-primary,btn-sm" HorizontalOptions="Start"/>
    </VerticalStackLayout>
</Border>

<!-- Colored card -->
<Border StyleClass="card,text-bg-primary">
    <Label Text="Primary card" StyleClass="on-primary"/>
</Border>

C# / MauiReactor

Border(
    VStack(
        Label("Card Title").Class(Bs.H5),
        Label("Content").Class(Bs.TextMuted)
    )
).Class(Bs.Card).Class(Bs.Shadow)

Badges

Badges use a Border container with a Label inside:

<Border StyleClass="badge,bg-primary">
    <Label Text="New" StyleClass="on-primary,small"/>
</Border>

Progress

<ProgressBar Progress="0.75"/>                              <!-- Primary (default) -->
<ProgressBar Progress="0.5" StyleClass="progress-success"/>
<ProgressBar Progress="0.25" StyleClass="progress-danger"/>

DynamicResource Keys

Colors

<BoxView Color="{DynamicResource Primary}"/>
<Border Stroke="{DynamicResource Outline}"/>
<Label TextColor="{DynamicResource OnBackground}"/>

Attached Properties

Alternative to StyleClass for handler-level styling (buttons, spacing, shadows). See references/attached-properties.md for details.

Theme Switching

// Switch theme at runtime:
BootstrapTheme.Apply("darkly");

Available Bootswatch themes: default, darkly, slate, flatly, sketchy, vapor, brite (or any Bootstrap 5 CSS).

Handling Theme Changes

BootstrapTheme.Apply() swaps the ResourceDictionary and fires BootstrapTheme.ThemeChanged. Controls using DynamicResource update automatically, but page backgrounds and any values read from BootstrapTheme.Current do not — you must listen and refresh.

XAML Pages

Subscribe to BootstrapTheme.ThemeChanged to update the page background (and any other BootstrapTheme.Current values) on theme switch:

public partial class MyPage : ContentPage
{
    public MyPage()
    {
        InitializeComponent();
        this.BackgroundColor = BootstrapTheme.Current.GetBackground();
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        BootstrapTheme.ThemeChanged += OnThemeChanged;
    }

    protected override void OnDisappearing()
    {
        BootstrapTheme.ThemeChanged -= OnThemeChanged;
        base.OnDisappearing();
    }

    private void OnThemeChanged(object? sender, EventArgs e)
    {
        this.BackgroundColor = BootstrapTheme.Current.GetBackground();
    }
}

MauiReactor Pages — BasePage Pattern

In MauiReactor, create a BasePage component that subscribes to ThemeChanged and calls Invalidate() to re-render with the new theme values:

abstract class BasePage : Component
{
    protected override void OnMounted()
    {
        BootstrapTheme.ThemeChanged += OnThemeChanged;
        base.OnMounted();
    }

    protected override void OnWillUnmount()
    {
        BootstrapTheme.ThemeChanged -= OnThemeChanged;
        base.OnWillUnmount();
    }

    private void OnThemeChanged(object? sender, EventArgs e) => Invalidate();

    public abstract VisualNode RenderContent();

    public override VisualNode Render()
    {
        return ContentPage(
            RenderContent()
        ).BackgroundColor(BootstrapTheme.Current.GetBackground());
    }
}

Then every page extends BasePage (or BasePage<TState> for stateful pages — same pattern with Component<TState>):

class ControlsPage : BasePage
{
    public override VisualNode RenderContent()
        => ScrollView(
            VStack(spacing: 24,
                Label("Controls").Class("h1"),
                Button("Primary").Class("btn-primary")
            ).Padding(20)
        );
}

Common Mistakes

❌ DON'T: Bare controls without StyleClass

<Button Text="Save"/>           <!-- No styling! -->
<Entry Placeholder="Name"/>     <!-- No styling! -->

✅ DO: Always apply StyleClass

<Button Text="Save" StyleClass="btn-primary"/>
<Entry Placeholder="Name" StyleClass="form-control"/>

❌ DON'T: Use wrong class on wrong control

<Entry StyleClass="btn-primary"/>        <!-- btn-* is for Button only -->
<Button StyleClass="form-control"/>      <!-- form-control is for inputs -->
<Label StyleClass="card"/>               <!-- card is for Border only -->

✅ DO: Match classes to control types

<Button StyleClass="btn-primary"/>
<Entry StyleClass="form-control"/>
<Border StyleClass="card"/>
<Label StyleClass="h4"/>

❌ DON'T: Forget text contrast on colored backgrounds

<Border StyleClass="text-bg-primary">
    <Label Text="Invisible text"/>      <!-- Text inherits dark color, invisible on blue -->
</Border>

✅ DO: Use on-variant classes for contrast text

<Border StyleClass="text-bg-primary">
    <Label Text="Visible text" StyleClass="on-primary"/>
</Border>

❌ DON'T: Use StaticResource for theme colors

<Label TextColor="{StaticResource Primary}"/>  <!-- Won't update on theme switch -->

✅ DO: Use DynamicResource

<Label TextColor="{DynamicResource Primary}"/>

❌ DON'T: Forget page background and theme change handling

public MyPage() { InitializeComponent(); }  // White bg, won't update on theme switch

✅ DO: Set background and subscribe to theme changes

See the Handling Theme Changes section above for the full XAML and MauiReactor patterns.

Control → StyleClass Quick Reference