<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <!--    <item-->
    <!--        android:left="15dp"-->
    <!--        android:right="15dp">-->

    <!-- 若不设置 gravity，则 Indicator 宽度会填满整个 item -->
    <item android:gravity="center_horizontal">
        <shape>
            <corners android:radius="@dimen/dp_8" />

            <size
                android:width="@dimen/dp_22"
                android:height="@dimen/dp_3" />
        </shape>
    </item>
</layer-list>