diff --git a/cmd/launcher/main.go b/cmd/launcher/main.go
index c355036..0740267 100644
--- a/cmd/launcher/main.go
+++ b/cmd/launcher/main.go
@@ -1,15 +1,11 @@
 package main
 
 import (
-	"fmt"
 	"log"
 
-	"fyne.io/fyne/v2/app"
-	"fyne.io/fyne/v2/container"
-	"fyne.io/fyne/v2/widget"
-
 	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/auth"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/config"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui"
 )
 
 // version is set via -ldflags at build time.
@@ -24,7 +20,11 @@ func main() {
 	}
 	log.Printf("Data directory: %s", root)
 
-	// Try to restore an existing session.
+	settings, err := config.Load()
+	if err != nil {
+		log.Fatalf("Failed to load settings: %v", err)
+	}
+
 	client, err := auth.NewFromConfig()
 	if err != nil {
 		log.Fatalf("Failed to create auth client: %v", err)
@@ -41,15 +41,5 @@ func main() {
 		log.Println("No valid session — login required")
 	}
 
-	// Bootstrap Fyne UI.
-	a := app.New()
-	w := a.NewWindow(fmt.Sprintf("MrixsCraft %s", version))
-	w.Resize(fyne.NewSize(900, 600))
-	w.CenterOnScreen()
-
-	w.SetContent(container.NewVBox(
-		widget.NewLabel(fmt.Sprintf("MrixsCraft Launcher %s", version)),
-	))
-
-	w.ShowAndRun()
+	ui.Launch(client, sess, settings)
 }
diff --git a/internal/ui/components/components.go b/internal/ui/components/components.go
index ecb3040..a7f9ec5 100644
--- a/internal/ui/components/components.go
+++ b/internal/ui/components/components.go
@@ -1,2 +1,94 @@
-// package components provides reusable Fyne widgets (avatar, progress bar).
+// package components provides reusable Fyne widgets for the launcher UI.
 package components
+
+import (
+	"image/color"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/canvas"
+	"fyne.io/fyne/v2/container"
+	"fyne.io/fyne/v2/widget"
+)
+
+// ServerCard displays a single modpack entry in the sidebar.
+func ServerCard(name string, selected bool, onTap func()) fyne.CanvasObject {
+	bg := canvas.NewRectangle(color.Transparent)
+	bg.SetMinSize(fyne.NewSize(180, 48))
+
+	label := widget.NewLabel(name)
+	label.TextStyle.Bold = selected
+
+	content := container.NewBorder(nil, nil,
+		nil, nil,
+		label,
+	)
+
+	card := container.NewStack(bg, content)
+
+	btn := widget.NewButton("", onTap)
+	btn.Importance = widget.LowImportance
+
+	return container.NewStack(card, btn)
+}
+
+// ProgressBar wraps widget.ProgressBar with show/hide helpers.
+type ProgressBar struct {
+	*widget.ProgressBar
+	hidden bool
+}
+
+// NewProgressBar creates a new progress bar initialized to 0 and hidden.
+func NewProgressBar() *ProgressBar {
+	pb := widget.NewProgressBar()
+	pb.Hide()
+	return &ProgressBar{
+		ProgressBar: pb,
+		hidden:      true,
+	}
+}
+
+// SetProgress sets the value [0…1] and shows the bar.
+func (pb *ProgressBar) SetProgress(v float64) {
+	pb.SetValue(v)
+	if pb.hidden {
+		pb.Show()
+		pb.hidden = false
+	}
+}
+
+// Done hides the progress bar and resets it.
+func (pb *ProgressBar) Done() {
+	pb.SetValue(0)
+	pb.Hide()
+	pb.hidden = true
+}
+
+// PlayButton creates the accent "PLAY" button.
+func PlayButton(onTap func()) *widget.Button {
+	btn := widget.NewButton("▶  PLAY", onTap)
+	btn.Importance = widget.HighImportance
+	return btn
+}
+
+// SettingsButton creates the small settings (gear) button.
+func SettingsButton(onTap func()) *widget.Button {
+	btn := widget.NewButton("⚙", onTap)
+	btn.Importance = widget.LowImportance
+	return btn
+}
+
+// LogoutButton creates the logout button.
+func LogoutButton(onTap func()) *widget.Button {
+	btn := widget.NewButton("Выйти", onTap)
+	btn.Importance = widget.LowImportance
+	return btn
+}
+
+// AvatarImage returns a placeholder avatar (64×64 colored square).
+// TODO: render 8×64 face from skin PNG.
+func AvatarImage() *canvas.Image {
+	img := canvas.NewImageFromResource(nil)
+	img.SetMinSize(fyne.NewSize(64, 64))
+	img.FillMode = canvas.ImageFillContain
+	return img
+}
diff --git a/internal/ui/screens/screens.go b/internal/ui/screens/screens.go
index a265dbd..8c45863 100644
--- a/internal/ui/screens/screens.go
+++ b/internal/ui/screens/screens.go
@@ -1,2 +1,193 @@
 // package screens implements application screens (login, main menu, settings).
 package screens
+
+import (
+	"fmt"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/container"
+	"fyne.io/fyne/v2/dialog"
+	"fyne.io/fyne/v2/layout"
+	"fyne.io/fyne/v2/widget"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/auth"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/components"
+)
+
+// Modpack represents a single server/modpack entry from the backend.
+type Modpack struct {
+	Slug string
+	Name string
+}
+
+// MainScreen builds the primary launcher window content.
+func MainScreen(
+	w fyne.Window,
+	client *auth.Client,
+	session *auth.Session,
+	serverList []Modpack,
+	onPlay func(),
+	onSettings func(),
+) fyne.CanvasObject {
+
+	// ── Sidebar (Left) ──────────────────────────────────────
+	serverLabels := make([]*widget.Label, len(serverList))
+	serverContainer := container.NewVBox()
+
+	for i, sp := range serverList {
+		label := widget.NewLabel(sp.Name)
+		serverLabels[i] = label
+		index := i
+		card := components.ServerCard(sp.Name, index == 0, func() {
+			for j, l := range serverLabels {
+				l.TextStyle.Bold = (j == index)
+				l.Refresh()
+			}
+		})
+		serverContainer.Add(card)
+	}
+
+	sidebar := container.NewVScroll(serverContainer)
+
+	// ── Center (background + info) ──────────────────────────
+	bg := widget.NewRichTextFromMarkdown(
+		"# Welcome to MrixsCraft\n\n" +
+			"Select a server from the left panel and press **PLAY**.\n\n" +
+			"---\n\n" +
+			"*Version: dev*",
+	)
+	center := container.NewMax(widget.NewCard("", "", bg))
+
+	// ── Bottom bar ──────────────────────────────────────────
+	avatar := components.AvatarImage()
+
+	displayName := "Not logged in"
+	if session != nil && session.Username != "" {
+		displayName = session.Username
+	}
+	usernameLabel := widget.NewLabel(displayName)
+
+	logoutBtn := components.LogoutButton(func() {
+		dialog.ShowConfirm(
+			"Logout",
+			"Are you sure you want to log out?",
+			func(confirmed bool) {
+				if confirmed {
+					_ = auth.Delete()
+					w.Close()
+				}
+			},
+			w,
+		)
+	})
+
+	bottomLeft := container.NewHBox(
+		avatar,
+		usernameLabel,
+		layout.NewSpacer(),
+		logoutBtn,
+	)
+
+	progress := components.NewProgressBar()
+
+	playBtn := components.PlayButton(onPlay)
+	settingsBtn := components.SettingsButton(onSettings)
+
+	bottomRight := container.NewHBox(
+		settingsBtn,
+		widget.NewSeparator(),
+		playBtn,
+	)
+
+	bottomCenter := container.NewMax(progress)
+
+	bottom := container.NewBorder(
+		nil, nil,
+		bottomLeft,
+		bottomRight,
+		bottomCenter,
+	)
+
+	// ── Assemble ────────────────────────────────────────────
+	return container.NewBorder(
+		nil,
+		bottom,
+		sidebar,
+		nil,
+		center,
+	)
+}
+
+// LoginScreen builds a modal login form.
+func LoginScreen(w fyne.Window, client *auth.Client, onLogin func(*auth.Session)) {
+	username := widget.NewEntry()
+	username.SetPlaceHolder("Username or email")
+
+	password := widget.NewPasswordEntry()
+	password.SetPlaceHolder("Password")
+
+	form := widget.NewForm(
+		widget.NewFormItem("Username", username),
+		widget.NewFormItem("Password", password),
+	)
+
+	dialog.ShowCustomConfirm(
+		"Login — MrixsCraft",
+		"Login",
+		"Cancel",
+		form,
+		func(confirmed bool) {
+			if !confirmed {
+				return
+			}
+			sess, err := client.Authenticate(username.Text, password.Text)
+			if err != nil {
+				dialog.ShowError(err, w)
+				return
+			}
+			if err := sess.Save(); err != nil {
+				dialog.ShowError(err, w)
+				return
+			}
+			onLogin(sess)
+		},
+		w,
+	)
+}
+
+// SettingsScreen builds the settings modal.
+func SettingsScreen(w fyne.Window, onSave func(memoryMB int, extraArgs string)) {
+	memorySlider := widget.NewSlider(1024, 16384)
+	memorySlider.Step = 512
+	memorySlider.Value = 4096
+
+	memLabel := widget.NewLabel("4096 MB")
+	memorySlider.OnChanged = func(v float64) {
+		memLabel.SetText(fmt.Sprintf("%.0f MB", v))
+	}
+
+	extraArgs := widget.NewMultiLineEntry()
+	extraArgs.SetPlaceHolder("e.g. -XX:+UseG1GC -XX:MaxGCPauseMillis=50")
+
+	content := container.NewVBox(
+		widget.NewLabelWithStyle("Memory (RAM)", fyne.TextAlignLeading, fyne.TextStyle{Bold: true}),
+		memLabel,
+		memorySlider,
+		widget.NewSeparator(),
+		widget.NewLabelWithStyle("Extra JVM arguments", fyne.TextAlignLeading, fyne.TextStyle{}),
+		extraArgs,
+	)
+
+	dialog.ShowCustomConfirm(
+		"Settings",
+		"Save",
+		"Cancel",
+		content,
+		func(confirmed bool) {
+			if confirmed {
+				onSave(int(memorySlider.Value), extraArgs.Text)
+			}
+		},
+		w,
+	)
+}
diff --git a/internal/ui/theme/theme.go b/internal/ui/theme/theme.go
index 4657750..ca8d9da 100644
--- a/internal/ui/theme/theme.go
+++ b/internal/ui/theme/theme.go
@@ -1,2 +1,92 @@
-// package theme defines the custom Fyne theme (Minecraft-style colors, fonts).
+// package theme defines a custom Fyne theme with Minecraft-inspired colors.
 package theme
+
+import (
+	"image/color"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/theme"
+)
+
+// MinecraftTheme is a dark theme inspired by Minecraft's UI palette.
+type MinecraftTheme struct{}
+
+var _ fyne.Theme = (*MinecraftTheme)(nil)
+
+// Color returns the named color from the Minecraft palette.
+func (t *MinecraftTheme) Color(name fyne.ThemeColorName, variant fyne.ThemeVariant) color.Color {
+	switch name {
+	case theme.ColorNameBackground:
+		return color.RGBA{R: 30, G: 30, B: 30, A: 255} // dark stone
+	case theme.ColorNameButton:
+		return color.RGBA{R: 100, G: 100, B: 100, A: 255} // stone gray
+	case theme.ColorNameDisabled:
+		return color.RGBA{R: 80, G: 80, B: 80, A: 255}
+	case theme.ColorNameDisabledButton:
+		return color.RGBA{R: 60, G: 60, B: 60, A: 255}
+	case theme.ColorNameError:
+		return color.RGBA{R: 200, G: 50, B: 50, A: 255}
+	case theme.ColorNameFocus:
+		return color.RGBA{R: 76, G: 175, B: 80, A: 255} // green accent
+	case theme.ColorNameForeground:
+		return color.RGBA{R: 220, G: 220, B: 220, A: 255} // light gray
+	case theme.ColorNameHover:
+		return color.RGBA{R: 76, G: 175, B: 80, A: 255} // green
+	case theme.ColorNameInputBackground:
+		return color.RGBA{R: 50, G: 50, B: 50, A: 255}
+	case theme.ColorNameInputBorder:
+		return color.RGBA{R: 80, G: 80, B: 80, A: 255}
+	case theme.ColorNameMenuBackground:
+		return color.RGBA{R: 40, G: 40, B: 40, A: 255}
+	case theme.ColorNameOverlayBackground:
+		return color.RGBA{R: 0, G: 0, B: 0, A: 180}
+	case theme.ColorNamePlaceHolder:
+		return color.RGBA{R: 150, G: 150, B: 150, A: 255}
+	case theme.ColorNamePressed:
+		return color.RGBA{R: 56, G: 142, B: 60, A: 255} // dark green
+	case theme.ColorNamePrimary:
+		return color.RGBA{R: 76, G: 175, B: 80, A: 255} // green
+	case theme.ColorNameScrollBar:
+		return color.RGBA{R: 80, G: 80, B: 80, A: 200}
+	case theme.ColorNameSeparator:
+		return color.RGBA{R: 60, G: 60, B: 60, A: 255}
+	case theme.ColorNameShadow:
+		return color.RGBA{R: 0, G: 0, B: 0, A: 128}
+	default:
+		return theme.DefaultTheme().Color(name, variant)
+	}
+}
+
+// Font returns the default font (custom TTF can be added later).
+func (t *MinecraftTheme) Font(style fyne.TextStyle) fyne.Resource {
+	return theme.DefaultTheme().Font(style)
+}
+
+// Icon returns the named icon resource.
+func (t *MinecraftTheme) Icon(name fyne.ThemeIconName) fyne.Resource {
+	return theme.DefaultTheme().Icon(name)
+}
+
+// Size returns the named size value.
+func (t *MinecraftTheme) Size(name fyne.ThemeSizeName) float32 {
+	switch name {
+	case theme.SizeNameCaptionText:
+		return 11
+	case theme.SizeNameInlineIcon:
+		return 20
+	case theme.SizeNamePadding:
+		return 4
+	case theme.SizeNameScrollBar:
+		return 12
+	case theme.SizeNameScrollBarSmall:
+		return 4
+	case theme.SizeNameText:
+		return 14
+	case theme.SizeNameHeadingText:
+		return 24
+	case theme.SizeNameSubHeadingText:
+		return 18
+	default:
+		return theme.DefaultTheme().Size(name)
+	}
+}
diff --git a/internal/ui/ui.go b/internal/ui/ui.go
index f915cce..2c4e93a 100644
--- a/internal/ui/ui.go
+++ b/internal/ui/ui.go
@@ -1,2 +1,55 @@
-// package ui contains Fyne GUI code (main window, theme, navigation).
+// package ui contains the Fyne GUI bootstrap and wiring.
 package ui
+
+import (
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/app"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/auth"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/config"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/screens"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/theme"
+)
+
+// Launch initialises the Fyne application with the Minecraft theme and shows the main window.
+func Launch(client *auth.Client, session *auth.Session, settings config.Settings) {
+	a := app.New()
+	a.Settings().SetTheme(&theme.MinecraftTheme{})
+
+	w := a.NewWindow("MrixsCraft")
+	w.Resize(fyne.NewSize(float32(settings.Width), float32(settings.Height)))
+	w.CenterOnScreen()
+
+	// TODO: fetch from /api/servers.json
+	serverList := []screens.Modpack{
+		{Slug: "hitech", Name: "HiTech 1.21"},
+		{Slug: "vanilla", Name: "Vanilla 1.20"},
+	}
+
+	onPlay := func() {
+		// TODO: launch selected modpack
+	}
+
+	onSettings := func() {
+		screens.SettingsScreen(w, func(memoryMB int, extraArgs string) {
+			settings.MemoryMB = memoryMB
+			settings.ExtraArgs = extraArgs
+			_ = config.Save(settings)
+		})
+	}
+
+	content := screens.MainScreen(w, client, session, serverList, onPlay, onSettings)
+	w.SetContent(content)
+
+	// If no session, show login modal after the window is rendered.
+	if session == nil {
+		w.Show()
+		screens.LoginScreen(w, client, func(sess *auth.Session) {
+			// Refresh UI with logged-in state.
+			content := screens.MainScreen(w, client, sess, serverList, onPlay, onSettings)
+			w.SetContent(content)
+		})
+	}
+
+	w.ShowAndRun()
+}