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احتمالا جایی رو به اشتباه وارد کردید من در هر حال براتون کدهای مربوطه قرار میدم

فایل styles.xml

<resources>
<style name="MyBottomNavigationView" parent="Widget.MaterialComponents.BottomNavigationView">
<item name="itemIconTint">@color/bottom_navigation_item_color</item>
<item name="itemTextColor">@color/bottom_navigation_item_color</item>
<item name="itemRippleColor">@color/bottom_navigation_ripple_color</item>
<item name="itemTextAppearanceActive">@style/ActiveItemBottomNavigationTextAppearance</item>
</style>
<style name="ActiveItemBottomNavigationTextAppearance" parent="TextAppearance.MyTheme.Caption">
<item name="fontFamily">@font/primary_bold</item>
<item name="android:fontFamily">@font/primary_bold</item>
</style>
<style name="Theme.Nike.AuthTheme.Button" parent="Theme.Nike.AuthTheme">
<item name="backgroundTint">?colorOnBackground</item>
<item name="android:textColor">@color/black</item>
<item name="cornerRadius">8dp</item>
<item name="android:fontFamily">@font/primary_bold</item>
</style>
<style name="Theme.Nike.AuthTheme.EditText" parent="Theme.Nike.AuthTheme">
<item name="android:background">@drawable/background_auth_et</item>
<item name="android:textColorHint">#48ffffff</item>
<item name="android:textColor">?colorOnBackground</item>
<item name="android:textSize">16sp</item>
<item name="android:minHeight">48dp</item>
<item name="android:paddingEnd">16dp</item>
<item name="android:paddingStart">16dp</item>
</style>
</resources>

themes.xml

<resources xmlns:tools="http://schemas.android.com/tools">
<!--  Base application theme.  -->
<style name="Theme.NikeStore" parent="Theme.MaterialComponents.DayNight.NoActionBar">
<!--  Primary brand color.  -->
<item name="colorPrimary">@color/blue</item>
<item name="colorOnPrimary">@color/white</item>
<!--  Secondary brand color.  -->
<item name="colorSecondary">@color/black</item>
<item name="colorOnSecondary">@color/white</item>
<!--  Status bar color.  -->
<item name="android:statusBarColor" tools:targetApi="l">@color/gray</item>
<item name="android:windowLightStatusBar" tools:targetApi="m">true</item>
<item name="fontFamily">@font/primary_regular</item>
<item name="windowBackgroundColorSub">#f5f5f5</item>
<!-- Material type attributes -->
<item name="textAppearanceHeadline1">@style/TextAppearance.MyTheme.Headline1</item>
<item name="textAppearanceHeadline2">@style/TextAppearance.MyTheme.Headline2</item>
<item name="textAppearanceHeadline3">@style/TextAppearance.MyTheme.Headline3</item>
<item name="textAppearanceHeadline4">@style/TextAppearance.MyTheme.Headline4</item>
<item name="textAppearanceHeadline5">@style/TextAppearance.MyTheme.Headline5</item>
<item name="textAppearanceHeadline6">@style/TextAppearance.MyTheme.Headline6</item>
<item name="textAppearanceSubtitle1">@style/TextAppearance.MyTheme.Subtitle1</item>
<item name="textAppearanceSubtitle2">@style/TextAppearance.MyTheme.Subtitle2</item>
<item name="textAppearanceBody1">@style/TextAppearance.MyTheme.Body1</item>
<item name="textAppearanceBody2">@style/TextAppearance.MyTheme.Body2</item>
<item name="textAppearanceButton">@style/TextAppearance.MyTheme.Button</item>
<item name="textAppearanceCaption">@style/TextAppearance.MyTheme.Caption</item>
<item name="textAppearanceOverline">@style/TextAppearance.MyTheme.Overline</item>
<!--  Customize your theme here.  -->
<item name="bottomNavigationStyle">@style/MyBottomNavigationView</item>
<item name="appBarLayoutStyle">
@style/Widget.MaterialComponents.AppBarLayout.Surface
</item>
<item name="dividerColor">@color/gray</item>
<item name="android:textColorSecondary">@color/darkGray</item>
<item name="android:lineSpacingExtra">6dp</item>
<item name="android:includeFontPadding">false</item>
</style>
<style name="Theme.Nike.AuthTheme" parent="Theme.NikeStore">
<item name="android:statusBarColor" tools:targetApi="lollipop">@color/black</item>
<item name="android:windowLightStatusBar" tools:targetApi="m">false</item>
<item name="android:windowBackground">@color/black</item>
<item name="colorOnBackground">@color/white</item>
<item name="colorOnSurface">@color/white</item>
<item name="materialButtonStyle">@style/Theme.Nike.AuthTheme.Button</item>
</style>
</resources>

type.xml

<resources>
<!-- Typography -->
<!--
Material’s type system supports 13 categories that, when combined, form the typescale. 
-->
<!--
This typescale is evident in the variety of text styles and sizes that appear on screen, 
-->
<!--
ranging from body copy to buttons. Type appears across the UI, in places such as in 
-->
<!-- components and on surfaces. -->
<!--
These styles should be used throughout your app when creating text views so all your 
-->
<!--
text is consistently styled and easily updated if design or product needs change. Each 
-->
<!--
style in the type scale can be customized by defining a style and overriding that 
-->
<!--
style's Material Theme attribute (?textAppearanceHeadline1, ?textAppearanceBody2, etc.) 
-->
<!--
in your app's theme. In this project, type attributes have already been overridden in 
-->
<!--
themes.xml and are set to the styles in this file, type.xml. These ?textAppearance* 
-->
<!--
theme attributes should be used in your layouts to set a TextView’s appearance instead 
-->
<!--
of fully qualified style references and in favor of manually setting text properties.
-->
<!--
Type on Android is themed by defining a custom TextAppearance for each type scale style. 
-->
<!--
Use standard TextAppearance attributes such as textSize, textColor, fontFamily, 
-->
<!--
letterSpacing, etc. to define a custom appearance for each and see how they are 
-->
<!-- applied globally across your app. -->
<style name="TextAppearance.MyTheme.Headline1" parent="TextAppearance.MaterialComponents.Headline1">
<!-- Your custom type style here -->
<item name="android:textColor">?colorPrimary</item>
</style>
<style name="TextAppearance.MyTheme.Headline2" parent="TextAppearance.MaterialComponents.Headline2">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Headline3" parent="TextAppearance.MaterialComponents.Headline3">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Headline4" parent="TextAppearance.MaterialComponents.Headline4">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Headline5" parent="TextAppearance.MaterialComponents.Headline5">
<!-- Your custom type style here -->
<item name="android:textSize">18sp</item>
<item name="android:textColor">?colorOnBackground</item>
</style>
<style name="TextAppearance.MyTheme.Headline6" parent="TextAppearance.MaterialComponents.Headline6">
<!-- Your custom type style here -->
<item name="fontFamily">@font/primary_bold</item>
<item name="android:fontFamily">@font/primary_bold</item>
<item name="android:textSize">16sp</item>
<item name="android:textColor">@color/black</item>
</style>
<style name="TextAppearance.MyTheme.Subtitle1" parent="TextAppearance.MaterialComponents.Subtitle1">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Subtitle2" parent="TextAppearance.MaterialComponents.Subtitle2">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Body1" parent="TextAppearance.MaterialComponents.Body1">
<!-- Your custom type style here -->
<item name="android:textColor">?colorOnSurface</item>
<item name="android:textSize">14sp</item>
</style>
<style name="TextAppearance.MyTheme.Body2" parent="TextAppearance.MaterialComponents.Body2">
<!-- Your custom type style here -->
<item name="android:textColor">?colorOnSurface</item>
<item name="android:textSize">12sp</item>
</style>
<style name="TextAppearance.MyTheme.Button" parent="TextAppearance.MaterialComponents.Button">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Caption" parent="TextAppearance.MaterialComponents.Caption">
<!-- Your custom type style here -->
</style>
<style name="TextAppearance.MyTheme.Overline" parent="TextAppearance.MaterialComponents.Overline">
<!-- Your custom type style here -->
</style>
</resources>

ممنون از توجه شما
من چک کردم و مشابه بود. عکس مربوط به کدم رو می‌فرستم براتون. ممنون می‌شم شما هم ملاحظه کنید.
اینکه می‌ره از فایل type.xml و از بخش headline6 اون textAppearance رو می‌گیره، مطمئن هستم. چون اندازه فونت داره ست می‌شه.
اما فونت رو از اون بخش نمی‌گیره و از theme.xml داره می‌گیره.
ممنون می‌شم متوجه اشتباهم شدید، بفرمایید.