The button in the sliding list is displayed in the center after being clicked

Example settings: (7 buttons are placed in the sliding list as an example, the number can be configured at will)
Script content:

using UnityEngine;
using UnityEngine.UI;

public class MTest : MonoBehaviour
{
    
    
    public RectTransform rec;
    public ScrollRect scrollRect;
    public int count = 7;
    public Button[] btns = new Button[7];
    public RectTransform btnRec;

    //按钮长度
    float itemWidth;
    //水平组件
    public HorizontalLayoutGroup hlGroup;
    //中间间隔长度
    float middleWidth;
    //左间隔
    float leftWidth;
    //右间隔
    float rightWidth;
    //显示长度
    float showWidth;

    private void Awake()
    {
    
    
        itemWidth = btnRec.rect.width;
        middleWidth = hlGroup.spacing;
        leftWidth = hlGroup.padding.left;
        rightWidth = hlGroup.padding.right;
        showWidth = rec.rect.width;

        btns[0].onClick.AddListener(() => OnClickBtn(0));
        btns[1].onClick.AddListener(() => OnClickBtn(1));
        btns[2].onClick.AddListener(() => OnClickBtn(2));
        btns[3].onClick.AddListener(() => OnClickBtn(3));
        btns[4].onClick.AddListener(() => OnClickBtn(4));
        btns[5].onClick.AddListener(() => OnClickBtn(5));
        btns[6].onClick.AddListener(() => OnClickBtn(6));
    }
    
    public void OnClickBtn(int index)
    {
    
    
        //总滑动长度
        //所有按钮长度 + 所有中间间隔长度 + 左边距离+ 右边距离 - 显示长度
        float allLength = itemWidth * count + middleWidth * (count - 1) + leftWidth + rightWidth - showWidth;
        //当前按钮总间隔长度
        //（一个按钮长度 + 一个间隔长度） * 当前按钮序号 + 一半按钮长度
        float simpleLength = (itemWidth + middleWidth) * index + itemWidth / 2;
        //所需移动的长度
        //左间隔 + 总间隔长度 - 一半显示距离
        float moveLength = leftWidth + simpleLength - showWidth / 2;
        //转成滑块位置  0~1
        float value = Mathf.Clamp(moveLength / allLength, 0f, 1f);
        scrollRect.horizontalNormalizedPosition = value;
    }
}