diff --git a/android/app/src/main/java/org/maturita/maturita/MainActivity.kt b/android/app/src/main/java/org/maturita/maturita/MainActivity.kt
index b0836e1..4198d25 100644
--- a/android/app/src/main/java/org/maturita/maturita/MainActivity.kt
+++ b/android/app/src/main/java/org/maturita/maturita/MainActivity.kt
@@ -16,10 +16,10 @@ import androidx.compose.foundation.layout.navigationBarsPadding
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.foundation.shape.RoundedCornerShape
-import androidx.compose.material3.ExperimentalMaterial3Api
-import androidx.compose.material3.ModalBottomSheet
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
-import androidx.compose.material3.rememberModalBottomSheetState
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.lightColorScheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.ui.Alignment
@@ -51,6 +51,7 @@ import org.maturita.maturita.ui.StatsIcon
 import org.maturita.maturita.ui.StatsScreen
 import org.maturita.maturita.ui.SubjectsScreen
 import org.maturita.maturita.ui.UnitMapScreen
+import org.maturita.maturita.data.ColorMode
 import org.maturita.maturita.ui.VocabExercise
 import org.maturita.maturita.ui.WelcomeScreen
 
@@ -64,9 +65,43 @@ class MainActivity : ComponentActivity() {
     }
 }
 
-@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun MaturitaApp(vm: AppViewModel) {
+    val p = vm.palette
+    val scheme = if (vm.mode == ColorMode.Dark) {
+        darkColorScheme(
+            primary = p.accent,
+            onPrimary = p.onAccent,
+            secondary = p.accent2,
+            background = p.base,
+            onBackground = p.text,
+            surface = p.mantle,
+            onSurface = p.text,
+            surfaceVariant = p.surface1,
+            onSurfaceVariant = p.subtext,
+            error = p.error,
+        )
+    } else {
+        lightColorScheme(
+            primary = p.accent,
+            onPrimary = p.onAccent,
+            secondary = p.accent2,
+            background = p.base,
+            onBackground = p.text,
+            surface = p.mantle,
+            onSurface = p.text,
+            surfaceVariant = p.surface1,
+            onSurfaceVariant = p.subtext,
+            error = p.error,
+        )
+    }
+    MaterialTheme(colorScheme = scheme) {
+        MaturitaAppBody(vm)
+    }
+}
+
+@Composable
+private fun MaturitaAppBody(vm: AppViewModel) {
     val p = vm.palette
     LaunchedEffect(Unit) { vm.checkUpdate(false) }
     BackHandler(vm.canGoBack || vm.searchOpen || vm.settingsOpen) {
@@ -184,11 +219,10 @@ fun MaturitaApp(vm: AppViewModel) {
         }
         if (vm.searchOpen) SearchOverlay(vm)
         if (vm.settingsOpen) {
-            ModalBottomSheet(
-                onDismissRequest = { vm.settingsOpen = false },
-                sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true),
-                containerColor = p.base,
-                shape = RoundedCornerShape(topStart = 20.dp, topEnd = 20.dp),
+            Box(
+                Modifier
+                    .fillMaxSize()
+                    .background(p.base),
             ) { SettingsSheet(vm) }
         }
     }
diff --git a/android/app/src/main/java/org/maturita/maturita/ui/Exercises.kt b/android/app/src/main/java/org/maturita/maturita/ui/Exercises.kt
index 912a2a3..dfed1f2 100644
--- a/android/app/src/main/java/org/maturita/maturita/ui/Exercises.kt
+++ b/android/app/src/main/java/org/maturita/maturita/ui/Exercises.kt
@@ -23,6 +23,7 @@ import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.SideEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateListOf
@@ -656,7 +657,9 @@ private fun ComboLine(
     revealed: Boolean,
     inline: Boolean = false,
 ) {
-    if (idx in expected.indices) expected[idx] = answer
+    SideEffect {
+        if (idx in expected.indices && expected[idx] != answer) expected[idx] = answer
+    }
     val p = vm.palette
     var open by remember { mutableStateOf(false) }
     val box = @Composable {
@@ -963,6 +966,7 @@ private fun PrefixMenu(value: String, p: Palette, onPick: (String) -> Unit) {
 fun LitQuizScreen(vm: AppViewModel, id: String) {
     val book = vm.content.book(id) ?: return
     val qs = book.arr("quiz")
+    if (qs.isEmpty()) return
     var idx by remember { mutableIntStateOf(0) }
     var score by remember { mutableIntStateOf(0) }
     var answered by remember { mutableStateOf(false) }
diff --git a/android/app/src/main/java/org/maturita/maturita/ui/PathMap.kt b/android/app/src/main/java/org/maturita/maturita/ui/PathMap.kt
index d2a8264..a0c57c6 100644
--- a/android/app/src/main/java/org/maturita/maturita/ui/PathMap.kt
+++ b/android/app/src/main/java/org/maturita/maturita/ui/PathMap.kt
@@ -126,6 +126,7 @@ fun PathMap(
     nodes: List<MapNode>,
     palette: Palette,
     litUntil: Float,
+    modifier: Modifier = Modifier,
     nodeSize: Float = 72f,
     mx: Float = 90f,
     my: Float = 110f,
@@ -139,8 +140,8 @@ fun PathMap(
     if (nodes.isEmpty()) return
     val density = LocalDensity.current
     fun Float.toDp(): androidx.compose.ui.unit.Dp = with(density) { this@toDp.toDp() }
-    BoxWithConstraints(Modifier.fillMaxSize()) {
-        val avail = constraints.maxWidth.toFloat()
+    BoxWithConstraints(modifier.fillMaxSize()) {
+        val avail = constraints.maxWidth.toFloat().coerceAtLeast(1f)
         val geo = serpentine(nodes.size, avail, mx, my, spac, gap, wave, lift)
         Box(
             Modifier
diff --git a/android/app/src/main/java/org/maturita/maturita/ui/Screens.kt b/android/app/src/main/java/org/maturita/maturita/ui/Screens.kt
index 16c82e9..710b0fa 100644
--- a/android/app/src/main/java/org/maturita/maturita/ui/Screens.kt
+++ b/android/app/src/main/java/org/maturita/maturita/ui/Screens.kt
@@ -7,10 +7,9 @@ import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
-import androidx.compose.foundation.layout.ExperimentalLayoutApi
-import androidx.compose.foundation.layout.FlowRow
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
@@ -22,7 +21,6 @@ import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.text.BasicTextField
 import androidx.compose.foundation.verticalScroll
-import androidx.compose.material3.LinearProgressIndicator
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Alignment
@@ -31,7 +29,6 @@ import androidx.compose.ui.draw.alpha
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.SolidColor
-import androidx.compose.ui.graphics.StrokeCap
 import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
@@ -108,49 +105,49 @@ private fun FeatureCard(vm: AppViewModel, t: String, b: String, l: String) {
     }
 }
 
-@OptIn(ExperimentalLayoutApi::class)
 @Composable
 fun SubjectsScreen(vm: AppViewModel) {
     val p = vm.palette
     Column(Modifier.fillMaxSize().padding(horizontal = 16.dp)) {
         PageTop(vm, { vm.back() }, vm.tr("subjects_title"), vm.tr("subjects_sub"))
-        androidx.compose.foundation.layout.BoxWithConstraints(Modifier.fillMaxSize()) {
-            val cell = (maxWidth - 12.dp) / 2
-            FlowRow(
-                Modifier
-                    .fillMaxSize()
-                    .verticalScroll(rememberScrollState())
-                    .padding(bottom = 24.dp),
-                maxItemsInEachRow = 2,
-                horizontalArrangement = Arrangement.spacedBy(12.dp),
-                verticalArrangement = Arrangement.spacedBy(12.dp),
-            ) {
-                vm.content.subjects.forEach { s ->
-                    val open = s.bool("open")
-                    Box(
-                        Modifier
-                            .width(cell)
-                            .height(132.dp)
-                            .clip(RoundedCornerShape(20.dp))
-                            .background(p.mantle)
-                            .border(1.dp, if (open) p.text.copy(0.08f) else p.text.copy(0.04f), RoundedCornerShape(20.dp))
-                            .alpha(if (open) 1f else 0.48f)
-                            .then(if (open) Modifier.clickable { vm.goPage(s.str("target")) } else Modifier)
-                            .padding(16.dp),
-                        contentAlignment = Alignment.Center,
-                    ) {
-                        Column(horizontalAlignment = Alignment.CenterHorizontally) {
-                            when (s.str("icon")) {
-                                "de" -> GermanFlag(44.dp)
-                                "wifi" -> WifiIcon(p.text, 36.dp)
-                                "chip" -> ChipIcon(p.text, 36.dp)
-                                "cz" -> CzechFlag(44.dp)
-                                else -> LockIcon(p.overlay, 22.dp)
+        Column(
+            Modifier
+                .weight(1f)
+                .fillMaxWidth()
+                .verticalScroll(rememberScrollState())
+                .padding(bottom = 24.dp),
+            verticalArrangement = Arrangement.spacedBy(12.dp),
+        ) {
+            vm.content.subjects.chunked(2).forEach { row ->
+                Row(Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(12.dp)) {
+                    row.forEach { s ->
+                        val open = s.bool("open")
+                        Box(
+                            Modifier
+                                .weight(1f)
+                                .height(132.dp)
+                                .clip(RoundedCornerShape(20.dp))
+                                .background(p.mantle)
+                                .border(1.dp, if (open) p.text.copy(0.08f) else p.text.copy(0.04f), RoundedCornerShape(20.dp))
+                                .alpha(if (open) 1f else 0.48f)
+                                .then(if (open) Modifier.clickable { vm.goPage(s.str("target")) } else Modifier)
+                                .padding(16.dp),
+                            contentAlignment = Alignment.Center,
+                        ) {
+                            Column(horizontalAlignment = Alignment.CenterHorizontally) {
+                                when (s.str("icon")) {
+                                    "de" -> GermanFlag(44.dp)
+                                    "wifi" -> WifiIcon(p.text, 36.dp)
+                                    "chip" -> ChipIcon(p.text, 36.dp)
+                                    "cz" -> CzechFlag(44.dp)
+                                    else -> LockIcon(p.overlay, 22.dp)
+                                }
+                                Spacer(Modifier.height(10.dp))
+                                Text(vm.tr(s.str("key")), color = p.text, fontSize = 13.sp, fontWeight = FontWeight.SemiBold, textAlign = TextAlign.Center)
                             }
-                            Spacer(Modifier.height(10.dp))
-                            Text(vm.tr(s.str("key")), color = p.text, fontSize = 13.sp, fontWeight = FontWeight.SemiBold, textAlign = TextAlign.Center)
                         }
                     }
+                    if (row.size == 1) Spacer(Modifier.weight(1f))
                 }
             }
         }
@@ -166,7 +163,16 @@ fun SettingsSheet(vm: AppViewModel) {
             .verticalScroll(rememberScrollState())
             .padding(20.dp),
     ) {
-        Text(vm.tr("settings_title"), color = p.text, fontSize = 22.sp, fontWeight = FontWeight.Bold)
+        Row(verticalAlignment = Alignment.CenterVertically) {
+            Text(
+                vm.tr("settings_title"),
+                color = p.text,
+                fontSize = 22.sp,
+                fontWeight = FontWeight.Bold,
+                modifier = Modifier.weight(1f),
+            )
+            PillButton(vm.tr("back"), p) { vm.settingsOpen = false }
+        }
         Spacer(Modifier.height(16.dp))
         Text(vm.tr("mode"), color = p.subtext, fontSize = 12.sp, fontWeight = FontWeight.SemiBold)
         Spacer(Modifier.height(6.dp))
@@ -233,14 +239,14 @@ fun StatsScreen(vm: AppViewModel) {
     val pct = if (sum.totalEx == 0) 0 else (100 * sum.doneEx / sum.totalEx)
     Column(Modifier.fillMaxSize().padding(horizontal = 16.dp)) {
         PageTop(vm, { vm.back() }, vm.tr("stats_title"), vm.tr("stats_sub"))
-        Column(Modifier.verticalScroll(rememberScrollState()).padding(bottom = 24.dp)) {
+        Column(Modifier.weight(1f).verticalScroll(rememberScrollState()).padding(bottom = 24.dp)) {
             Row(Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(10.dp)) {
                 Metric(p, vm.tr("stats_ex_label"), vm.fmt("stats_ex_fmt", sum.doneEx, sum.totalEx), Modifier.weight(1f))
                 Metric(p, vm.tr("stats_pct_label"), vm.fmt("stats_pct_fmt", pct), Modifier.weight(1f))
                 Metric(p, vm.tr("stats_units_label"), vm.fmt("stats_units_fmt", sum.doneUnits, sum.openUnits), Modifier.weight(1f))
             }
             Spacer(Modifier.height(10.dp))
-            LinearProgressIndicator(pct / 100f, Modifier.fillMaxWidth().height(8.dp).clip(CircleShape), p.accent, p.surface1, StrokeCap.Round)
+            ProgressBar(pct / 100f, p, 8.dp)
             Spacer(Modifier.height(20.dp))
             Text(vm.tr("stats_section"), color = p.subtext, fontSize = 12.sp, fontWeight = FontWeight.SemiBold)
             Spacer(Modifier.height(8.dp))
@@ -258,11 +264,7 @@ fun StatsScreen(vm: AppViewModel) {
                         )
                         if (open && part.totalEx > 0) {
                             Spacer(Modifier.height(8.dp))
-                            LinearProgressIndicator(
-                                part.doneEx / part.totalEx.toFloat(),
-                                Modifier.fillMaxWidth().height(6.dp).clip(CircleShape),
-                                p.accent, p.surface1, StrokeCap.Round,
-                            )
+                            ProgressBar(part.doneEx / part.totalEx.toFloat(), p, 6.dp)
                         }
                     }
                 }
@@ -271,6 +273,24 @@ fun StatsScreen(vm: AppViewModel) {
     }
 }
 
+@Composable
+private fun ProgressBar(fraction: Float, p: org.maturita.maturita.data.Palette, barHeight: androidx.compose.ui.unit.Dp) {
+    Box(
+        Modifier
+            .fillMaxWidth()
+            .height(barHeight)
+            .clip(CircleShape)
+            .background(p.surface1),
+    ) {
+        Box(
+            Modifier
+                .fillMaxHeight()
+                .fillMaxWidth(fraction.coerceIn(0f, 1f))
+                .background(p.accent),
+        )
+    }
+}
+
 @Composable
 private fun Metric(p: org.maturita.maturita.data.Palette, label: String, value: String, modifier: Modifier) {
     CardBox(p, modifier) {
@@ -342,7 +362,7 @@ fun SearchOverlay(vm: AppViewModel) {
         if (hits.isEmpty()) {
             Text(if (q.isEmpty()) vm.tr("search_hint") else vm.tr("search_empty"), color = p.subtext)
         } else {
-            Column(Modifier.verticalScroll(rememberScrollState()), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+            Column(Modifier.weight(1f).verticalScroll(rememberScrollState()), verticalArrangement = Arrangement.spacedBy(8.dp)) {
                 hits.forEach { hit ->
                     CardBox(p, Modifier.fillMaxWidth().clickable {
                         if (!hit.locked) {
@@ -409,6 +429,7 @@ fun RoadmapScreen(vm: AppViewModel) {
     Column(Modifier.fillMaxSize().padding(horizontal = 12.dp)) {
         PageTop(vm, { vm.back() }, vm.tr("roadmap_title"), vm.tr("roadmap_sub"))
         PathMap(
+            modifier = Modifier.weight(1f),
             nodes = vm.content.german.mapIndexed { i, u ->
                 val unlocked = u.bool("unlocked")
                 val names = u.strs("names")
@@ -438,6 +459,7 @@ fun UnitMapScreen(vm: AppViewModel, unitId: Int) {
         PageTop(vm, { vm.back() }, u.str("title"), vm.tr(u.str("sub")))
         val next = names.indices.firstOrNull { !vm.progress.germanDone(unitId, it + 1) }
         PathMap(
+            modifier = Modifier.weight(1f),
             nodes = names.mapIndexed { i, name ->
                 val n = i + 1
                 MapNode(
@@ -503,7 +525,7 @@ fun LessonMapScreen(
 ) {
     Column(Modifier.fillMaxSize().padding(horizontal = 12.dp)) {
         PageTop(vm, { vm.back() }, title, sub)
-        PathMap(nodes, vm.palette, litUntil, nodeSize = 64f, spac = 150f, mx = 70f)
+        PathMap(nodes, vm.palette, litUntil, modifier = Modifier.weight(1f), nodeSize = 64f, spac = 150f, mx = 70f)
     }
 }
 
diff --git a/android/app/src/main/java/org/maturita/maturita/update/Updater.kt b/android/app/src/main/java/org/maturita/maturita/update/Updater.kt
index 74205ab..dad9196 100644
--- a/android/app/src/main/java/org/maturita/maturita/update/Updater.kt
+++ b/android/app/src/main/java/org/maturita/maturita/update/Updater.kt
@@ -66,6 +66,11 @@ class Updater(private val app: Application) {
                 val dir = File(app.cacheDir, "updates").apply { mkdirs() }
                 val apk = File(dir, "maturita.apk")
                 download(url, apk)
+                if (!isApk(apk)) {
+                    apk.delete()
+                    emit(cb, UpdateState("error", messageKey = "update_err_download", messageArg = null))
+                    return@execute
+                }
                 val uri = FileProvider.getUriForFile(app, "${app.packageName}.files", apk)
                 val intent = Intent(Intent.ACTION_VIEW).apply {
                     setDataAndType(uri, "application/vnd.android.package-archive")
@@ -79,6 +84,15 @@ class Updater(private val app: Application) {
         }
     }
 
+    private fun isApk(file: File): Boolean {
+        if (file.length() < 1_000_000L) return false
+        file.inputStream().use { input ->
+            val header = ByteArray(2)
+            if (input.read(header) != 2) return false
+            return header[0] == 'P'.code.toByte() && header[1] == 'K'.code.toByte()
+        }
+    }
+
     private fun get(url: String): String {
         val c = (URL(url).openConnection() as HttpURLConnection).apply {
             connectTimeout = 15000