tachiyomi/app/src/main/res/values-v21/themes.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <!--===========-->
    <!-- Main Theme-->
    <!--===========-->
    <style name="Theme.Tachiyomi" parent="Theme.Base">
        <!-- Attributes specific for SDK 21 and up  -->
        <item name="android:windowDrawsSystemBarBackgrounds">true</item>
        <item name="android:statusBarColor">@android:color/transparent</item>
        <item name="android:navigationBarColor">@color/colorPrimaryDark</item>
    </style>

    <!--============-->
    <!-- Dark Theme -->
    <!--============-->
    <style name="Theme.Tachiyomi.Dark" parent="Theme.Base.Dark">
        <!-- Attributes specific for SDK 21 and up  -->
        <item name="android:windowDrawsSystemBarBackgrounds">true</item>
        <item name="android:statusBarColor">@android:color/transparent</item>
        <item name="android:navigationBarColor">@color/colorPrimaryDark</item>
    </style>

    <!--==============-->
    <!-- Reader Theme -->
    <!--==============-->
    <style name="Theme.Reader" parent="Theme.Base.Reader">
        <!-- Attributes specific for SDK 21 and up  -->
        <item name="android:statusBarColor">?colorPrimaryDark</item>
        <item name="android:navigationBarColor">?colorPrimaryDark</item>
    </style>

</resources>