CSS实现DIV居中异常求助：优化样式并设宽度为75%

问题描述 #

DIV无法正确居中，经排查是CSS配置导致。需要修正CSS代码，移除不必要声明，实现DIV水平居中且宽度设置为75%。

当前CSS代码 #

.css_main_popup {
    transition: opacity 10ms;
    visibility: hidden;
    position: absolute;
    top: 10px;
    right: 10px;
    font-size: 30px;
    font-weight: bold;
    text-decoration: none;
    color: #333;
    margin: auto;
    margin-left: auto;
    margin-right: auto;
    padding: 10px;
    background: #fff;
    border-radius: 5px;
    width: 95%;
    height: 90%;
    overflow: auto;
    align-self: center;
  }

当前HTML代码 #

<!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>SMT Explorer</title>
        <link rel="stylesheet" href="explorer.css">
        <link rel="stylesheet" href="main.css">
    </head>

    <body>
        <div id="main_div" style="position: relative; "></div>

        <div id="popup_factory" class="css_main_popup">
            <a class="css_close_popup" href="#" style='text-align:right' onclick="CloseFPopup()">&times;</a>
        </div>

        <div id="popup_stations" class="css_main_popup">
            <a class="css_close_popup" href="#" style='text-align:right' onclick="CloseSPopup()">&times;</a>
        </div>

        <script type="text/javascript" src="explorer.js"></script>
    </body>

</html>

修正后的CSS代码 #

.css_main_popup {
    transition: opacity 10ms;
    visibility: hidden;
    position: absolute;
    top: 10px;
    font-size: 30px;
    font-weight: bold;
    text-decoration: none;
    color: #333;
    margin: 0 auto;
    padding: 10px;
    background: #fff;
    border-radius: 5px;
    width: 75%;
    height: 90%;
    overflow: auto;
    left: 0;
    right: 0;
}

关键修改说明 #

• 移除right: 10px：该声明强制元素固定在右侧，直接阻断居中效果
• 简化margin为margin: 0 auto：替代重复的margin-left/right: auto，实现水平居中
• 添加left: 0和right: 0：绝对定位元素需同时设置左右为0，才能让margin: auto生效实现水平居中
• 将width: 95%改为width: 75%：满足宽度要求
• 移除align-self: center：该属性属于flex布局范畴，对绝对定位元素无效

内容的提问来源于stack exchange，提问作者Mi Po