我想将img垂直居中。是的，关于stackoverflow的这个问题有很多问题，但是它们并没有帮助我。图像是logo.svg，css文件中名为logo-img2的类为空。
HTML和自举程序4：
<!doctype html>
<html <?php language_attributes(); ?> class="no-js">
<head>
<meta charset="<?php bloginfo('charset'); ?>">
<title><?php wp_title(''); ?><?php if(wp_title('', false)) { echo ' :'; } ?> <?php bloginfo('name'); ?></title>
<link href="//www.google-analytics.com" rel="dns-prefetch">
<link href="<?php echo get_template_directory_uri(); ?>/img/icons/favicon.ico" rel="shortcut icon">
<link href="<?php echo get_template_directory_uri(); ?>/img/icons/touch.png" rel="apple-touch-icon-precomposed">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="<?php bloginfo('description'); ?>">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
Wordpress代码：
<?php wp_head(); ?>
<script>
// conditionizr.com
// configure environment tests
conditionizr.config({
assets: '<?php echo get_template_directory_uri(); ?>',
tests: {}
});
</script>
</head>
<body <?php body_class(); ?>>
<!-- wrapper -->
<div class="wrapper">
<!-- header -->
<header class="header clear sticky-top" role="banner">
<!-- logo -->
<div class="logo">
这是svg呼叫者代码：
<!-- nav -->
<span class="nav" role="navigation" ">
<a href="<?php echo home_url(); ?>">
<!-- svg logo - toddmotto.com/mastering-svg-use-for-a-retina-web-fallbacks-with-png-script -->
<img src="<?php echo get_template_directory_uri(); ?>/img/logo.svg" alt="Logo" class="logo-img2" style="max-height: 30px; ">
</a>
<span style="float: left"><?php html5blank_nav(); ?></span> </span>
<!-- <span class="nav" role="navigation" style="float:right"> <?php //html5blank_nav2(); ?> </span>
<!-- /nav -->
</div>
<!-- /logo -->
</header>
<!-- /header -->
怎么办？
首先，您应该知道标题元素的大小，然后添加样式，其中x-标题的高度，y-img的高度：
.logo-img2 {
margin: calc((x - y) / 2) 0;
}