Flex布局中设置了容器留白均分，不能在设置项目居中嘛

问题遇到的现象和发生背景

Flex布局中设置了容器留白均分，不能在设置项目居中

问题相关代码，请勿粘贴截图
<div>
        <a href="">
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
            <span></span>
        </a>
   </div>



a {
    display: flex;
    margin-bottom: 20px;
    position: relative;
    left: 50%;
    top: 200px;
    
    width: 50px;
    height: 50px;
    background-color: aliceblue;
    padding: 10px;
    border-radius: 5px;
}
a span {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background-color: black;
}
a:nth-child(3) {
    flex-direction: column;
}
a:nth-child(3) {
    justify-content: space-evenly;
}

a:nth-child(3) span:nth-child(2) {
    justify-content: center;
    align-items: center;
    background-color: aquamarine;
}
运行结果及报错内容

三个span主轴方向均匀排列，但是第二个不能去中间，第三个不能去最右

我的解答思路和尝试过的方法

添加第二个span的背景颜色是变的，说明是主轴方向的位置属性冲突，但是自学css找不出原因

我想要达到的结果

想做出类似骰子的三点样式。


<style>
    div {
        display: flex;
    }
a {
    display: flex;
    margin-bottom: 20px;
    /* position: relative; */
    left: 50%;
    top: 200px;
    
    width: 50px;
    height: 50px;
    background-color: aliceblue;
    padding: 10px;
    border-radius: 5px;
}
a span {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background-color: black;
}
a:nth-child(3) {
    flex-direction: column;
}
a:nth-child(3) {
    justify-content: space-evenly;
}
 
a:nth-child(3) span:nth-child(2) {
    justify-content: center;
    align-items: center;
    background-color: aquamarine;
}
 
</style>
<div>
        <a href="">
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
            <span></span>
        </a>
   </div>
 
 


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        a {
            display: block;
            margin-bottom: 20px;
            /* position: relative;
            left: 50%;
            top: 200px; */
            
            width: 50px;
            height: 50px;
            background-color: aliceblue;
            padding: 10px;
            border-radius: 5px;
        }
        a span {
            display: block;
            width: 12px;
            height: 12px;
            border-radius: 50%;
            background-color: black;
        }
        .one, .two {
            display: flex;
            justify-content: space-around;
        } 
    </style>
</head>
<body>
    <div>
        <a href="">
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
        </a>
        <a href="">
            <div class="one">
                <span></span>
            </div>
            <div class="two">
                <span></span>
                <span></span>
            </div>
        </a>
   </div>
</body>
</html>

img


<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        a {
            display: flex;
            align-items: center;
            justify-content: space-evenly;
            margin: 20px auto;
            padding: 10px;
            width: 50px;
            height: 50px;
            border-radius: 5px;
            background-color: aliceblue;
        }

        a span {
            width: 12px;
            height: 12px;
            border-radius: 50%;
            background-color: black;
        }
        a:nth-child(3) span:nth-child(1){
            align-self: flex-start;
        }

        a:nth-child(3) span:nth-child(2) {
            background-color: aquamarine;
        }
        a:nth-child(3) span:nth-child(3){
            align-self: flex-end;
        }
    </style>
</head>

<body>
    <div>
        <a href="">
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
        </a>
        <a href="">
            <span></span>
            <span></span>
            <span></span>
        </a>
    </div>


</body>

</html>