If you want to customize seekbar in Android then follow the steps mentioned below:-

1) To customize seekbar background create a new xml file in your project's drawable folder .

seekbar_background.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >

    <gradient
        android:angle="90"
        android:centerColor="#fff"
        android:endColor="#fff"
        android:startColor="#fff" />

    <corners android:radius="2dp" />

    <stroke
        android:width="2dp"
        android:color="#fff" />
    <stroke
        android:width="2dp"
        android:color="#fff" />

</shape>

2) To customize seekbar progress create a new xml file in your project's drawable folder .

seekbar_progress.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >

    <gradient
        android:angle="90"
        android:centerColor="#7FBD5C"
        android:endColor="#7FBD5C"
        android:startColor="#7FBD5C" />

    <corners android:radius="1dp" />

    <stroke
        android:width="1dp"
        android:color="#fff" />
    <stroke
        android:width="1dp"
        android:color="#fff" />

</shape>

3) Now create a new xml file in your project's drawable folder name it custom_seekbar.xml.

custom_seekbar.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@android:id/background"
        android:drawable="@drawable/seekbar_background"/>
    <item android:id="@android:id/progress">
        <clip android:drawable="@drawable/seekbar_progress" />
    </item>

</layer-list>

4) Now to customize seekbar thumb create another xml file in your project's drawable folder.

custom_seekbar_thumb.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"

    android:shape="oval" >

    <gradient
        android:angle="45"
        android:gradientRadius="20mm"
        android:endColor="#7FBD5C"
        android:startColor="#7FBD5C"
        />

    <size
        android:height="0dp"
        android:width="0dp" />

</shape>

5) Now impliment these custom xml file in seekbar tag.

<SeekBar
            android:id="@+id/CapacitySeekBar"
            android:layout_width="match_parent"
            android:layout_height="20dp"
            android:layout_marginLeft="17dp"
            android:layout_marginRight="17dp"
            android:layout_marginBottom="10dp"
            android:thumb="@drawable/custom_seekbar_thumb"
            android:progress="2"
            android:progressDrawable="@drawable/custom_seekbar"
            android:enabled="false"
            android:max="5"/>