发生了一件非常奇怪的事情，我正在使用正确的类和样式将我的h1和段落居中。我的col-12包含H1的div和另一个包含段落的col-12的div应该在Row div的中心彼此靠近。
为什么即使我使用对齐内容中心和对齐项目中心也无法正常工作？谢谢！
*{
margin: 0;
padding: 0;
box-sizing: border-box;
}
body{
background-color: pink;
}
.red-b{border: 4px solid red;}
.blue-b{border: 4px solid blue;}
.yellow-b{border: 4px solid yellow;}
.green-b{border: 4px solid green;}
.orange-b{border: 4px solid orange;}
.black-b{border: 4px solid black;}
/* HEADER */
.main-header{
background-image: url('header-photo.jpg');
height: 100vh;
background-size: cover;
background-repeat: no-repeat;
background-position: center center;
}
.main-header a{
color: #fff;
}
.header-banner{
height: 80vh;
}
h1{
color: white;
font-size: 100px;
text-align: center;
font-weight: 700;
}
@media only screen and (max-width: 1200px) {
h1{
color: red;
}
}
@media only screen and (max-width: 992px) {
h1{
color: yellow;
font-size: 70px;
}
}
/*MAIN*/
/*FOOTER*/<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<title>Hello, world!</title>
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<header class="main-header">
<div class="container">
<nav class="navbar navbar-expand-lg navbar-dark">
<a class="navbar-brand" href="#">START BOOTSTRAP</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav ml-auto">
<li class="nav-item active">
<a class="nav-link" href="#">About <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Services</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Portfolio</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Contact</a>
</li>
</ul>
</div>
</nav>
<div class="header-banner row justify-content-center align-items-center blue-b">
<div class="col-12 red-b">
<h1>YOUR FAVORITE SOURCE OF FREE BOOTSTRAP THEMES</h1>
</div>
<div class="col-12 yellow-b">
<p class="header-paragraph text-center">lorem ipsum blablabla Montreal Canada</p>
</div>
</div> <!-- /.row -->
</div><!-- /.container -->
</header>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<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>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>
</html>
答案 0 :(得分：1)
您需要考虑align-content-center（https://getbootstrap.com/docs/4.1/utilities/flex/#align-content）
*{
margin: 0;
padding: 0;
box-sizing: border-box;
}
body{
background-color: pink;
}
.red-b{border: 4px solid red;}
.blue-b{border: 4px solid blue;}
.yellow-b{border: 4px solid yellow;}
.green-b{border: 4px solid green;}
.orange-b{border: 4px solid orange;}
.black-b{border: 4px solid black;}
/* HEADER */
.main-header{
background-image: url('header-photo.jpg');
height: 100vh;
background-size: cover;
background-repeat: no-repeat;
background-position: center center;
}
.main-header a{
color: #fff;
}
.header-banner{
height: 80vh;
}
h1{
color: white;
font-size: 100px;
text-align: center;
font-weight: 700;
}
@media only screen and (max-width: 1200px) {
h1{
color: red;
}
}
@media only screen and (max-width: 992px) {
h1{
color: yellow;
font-size: 70px;
}
}
/*MAIN*/
/*FOOTER*/<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<title>Hello, world!</title>
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<header class="main-header">
<div class="container">
<nav class="navbar navbar-expand-lg navbar-dark">
<a class="navbar-brand" href="#">START BOOTSTRAP</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav ml-auto">
<li class="nav-item active">
<a class="nav-link" href="#">About <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Services</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Portfolio</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Contact</a>
</li>
</ul>
</div>
</nav>
<div class="header-banner row justify-content-center align-items-center blue-b align-content-center">
<div class="col-12 red-b">
<h1>YOUR FAVORITE SOURCE OF FREE BOOTSTRAP THEMES</h1>
</div>
<div class="col-12 yellow-b">
<p class="header-paragraph text-center">lorem ipsum blablabla Montreal Canada</p>
</div>
</div> <!-- /.row -->
</div><!-- /.container -->
</header>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<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>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>
</html>