tachiyomi/app/src/main/res/layout/reader_activity.xml

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center">

    <FrameLayout
        android:id="@+id/reader_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <FrameLayout
            android:id="@+id/viewer_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

        <com.google.android.material.progressindicator.CircularProgressIndicator
            android:id="@+id/please_wait"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:indeterminate="true"
            android:visibility="gone"
            app:indicatorSize="56dp"
            tools:visibility="visible" />

        <eu.kanade.tachiyomi.ui.reader.PageIndicatorTextView
            android:id="@+id/page_number"
            style="@style/TextAppearance.Regular.Caption"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|center_horizontal"
            android:padding="4dp"
            android:textDirection="ltr"
            android:textStyle="bold" />

    </FrameLayout>

    <eu.kanade.tachiyomi.ui.reader.ReaderColorFilterView
        android:id="@+id/color_overlay"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone" />

    <FrameLayout
        android:id="@+id/reader_menu"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:theme="?attr/actionBarTheme"
        android:visibility="invisible"
        tools:visibility="visible">

        <com.google.android.material.appbar.MaterialToolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary" />

        <LinearLayout
            android:id="@+id/reader_menu_bottom"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            android:orientation="vertical">

            <LinearLayout
                android:id="@+id/reader_nav"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginBottom="16dp"
                android:layoutDirection="ltr"
                android:orientation="horizontal">

                <ImageButton
                    android:id="@+id/left_chapter"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:layout_marginEnd="8dp"
                    android:background="@drawable/reader_seekbar_background"
                    android:contentDescription="@string/action_previous_chapter"
                    android:padding="@dimen/material_layout_keylines_screen_edge_margin"
                    app:srcCompat="@drawable/ic_skip_previous_24dp"
                    app:tint="?attr/colorOnPrimary" />

                <LinearLayout
                    android:id="@+id/reader_seekbar"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/reader_seekbar_button"
                    android:paddingStart="8dp"
                    android:paddingEnd="8dp">

                    <TextView
                        android:id="@+id/left_page_text"
                        android:layout_width="32dp"
                        android:layout_height="match_parent"
                        android:gravity="center"
                        android:textColor="?attr/colorOnPrimary"
                        android:textSize="15sp"
                        tools:text="1" />

                    <!--
                        Wonky way of setting height due to issues with horizontally centering the thumb in Android 5.
                        See https://stackoverflow.com/questions/15701767/android-thumb-is-not-centered-in-seekbar
                    -->
                    <eu.kanade.tachiyomi.ui.reader.ReaderSeekBar
                        android:id="@+id/page_seekbar"
                        android:layout_width="0dp"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:maxHeight="?attr/actionBarSize"
                        android:minHeight="?attr/actionBarSize" />

                    <TextView
                        android:id="@+id/right_page_text"
                        android:layout_width="32dp"
                        android:layout_height="match_parent"
                        android:gravity="center"
                        android:textColor="?attr/colorOnPrimary"
                        android:textSize="15sp"
                        tools:text="15" />

                </LinearLayout>

                <ImageButton
                    android:id="@+id/right_chapter"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:layout_marginStart="8dp"
                    android:background="@drawable/reader_seekbar_button"
                    android:contentDescription="@string/action_next_chapter"
                    android:padding="@dimen/material_layout_keylines_screen_edge_margin"
                    app:srcCompat="@drawable/ic_skip_next_24dp"
                    app:tint="?attr/colorOnPrimary" />

            </LinearLayout>

            <androidx.constraintlayout.widget.ConstraintLayout
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:layout_gravity="bottom"
                android:background="?attr/colorPrimary">

                <ImageButton
                    android:id="@+id/action_custom_filter"
                    android:layout_width="wrap_content"
                    android:layout_height="match_parent"
                    android:background="?selectableItemBackgroundBorderless"
                    android:contentDescription="@string/custom_filter"
                    android:padding="@dimen/material_layout_keylines_screen_edge_margin"
                    app:layout_constraintEnd_toStartOf="@id/action_settings"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent"
                    app:srcCompat="@drawable/ic_brightness_4_24dp"
                    app:tint="?attr/colorOnPrimary" />

                <ImageButton
                    android:id="@+id/action_settings"
                    android:layout_width="wrap_content"
                    android:layout_height="match_parent"
                    android:background="?selectableItemBackgroundBorderless"
                    android:contentDescription="@string/action_settings"
                    android:padding="@dimen/material_layout_keylines_screen_edge_margin"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toEndOf="@id/action_custom_filter"
                    app:layout_constraintTop_toTopOf="parent"
                    app:srcCompat="@drawable/ic_settings_24dp"
                    app:tint="?attr/colorOnPrimary" />

            </androidx.constraintlayout.widget.ConstraintLayout>

        </LinearLayout>

    </FrameLayout>

    <View
        android:id="@+id/brightness_overlay"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>