当我遇到一个无法找到解决方法的问题时，我正在创建一个自举网站作为挑战。
在jumbotron中我有一个带有文本字段和提交按钮的表单。
文本字段还有一个插件（input-group-addon）
没有任何图像插件完全放置在应有的位置但是当我添加图像时，插件会从文本字段移开一个像素。
.bg {
background-image: url("http://www.zastavki.com/pictures/originals/2013/Photoshop_Image_of_the_horse_053857_.jpg");
text-align: center;
color: white;
}
.jumbotron form {
text-align: none;
}
.jumbotron hr {
background-color: white;
}<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js"></script>
<body style="position: relative;" data-spy="scroll" data-target="#navBar">
<nav id="navBar" class="navbar navbar-toggleable-md navbar-light bg-faded">
<button class="navbar-toggler navbar-toggler-right" 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>
<a class="navbar-brand" href="#">My App</a>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mr-auto">
<li class="nav-item active">
<a class="nav-link" href="#home">Home <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Features</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Download</a>
</li>
</ul>
<form class="form-inline my-2 my-lg-0">
<input class="form-control mr-sm-2" type="text" placeholder="Search">
<button class="btn btn-success my-2 my-sm-0" type="submit">Search</button>
</form>
</div>
</nav>
<div class="jumbotron bg">
<h1 class="display-3">My Amazing App!</h1>
<p class="lead">The MAIN reason for YOU to download THIS app on your handheld Android or iOS device.</p>
<hr class="my-4">
<p class="lead">Want to learn more ? Join our Mailing List and get a free bonus.</p>
<form class="form-inline justify-content-center">
<label class="sr-only" for="email">Email</label>
<div class="input-group mb-2 mr-sm-2 mb-sm-0">
<div class="input-group-addon">@</div>
<input style="width: 350px;" type="email" class="form-control" id="email" placeholder="Your Email">
</div>
<button type="submit" class="btn btn-primary">Sign Up</button>
</form>
</div>
答案 0 :(得分：0)
Bootstrap 4仍在测试版中，为.form-control类应用了一个高度透明的边框。您的示例突出显示了在对具有深色背景的容器使用输入元素时，这可能会产生意外结果。 Bootstrap 4的默认样式是：
.form-control {
border-color: rgba(0, 0, 0, 0.15);
}
这是一个近乎最大透明度的黑色边框。正如您所发现的那样，在黑暗的背景下渲染将无法达到预期的效果。
我已经附加了一个自定义类来覆盖.stat-control类的Bootstrap 4的默认边框颜色。应用于您的示例，仅当类.bg也应用于jumbotron时，它才有效。
.bg .form-control.solid-gray-border {
border-color: rgb(222,222,222);
}
.bg {
background-image: url("http://www.zastavki.com/pictures/originals/2013/Photoshop_Image_of_the_horse_053857_.jpg");
text-align: center;
color: white;
}
.jumbotron form {
text-align: none;
}
.jumbotron hr {
background-color: white;
}
.bg .form-control.solid-gray-border {
border-color: rgb(222,222,222);
}<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js"></script>
<body style="position: relative;" data-spy="scroll" data-target="#navBar">
<nav id="navBar" class="navbar navbar-toggleable-md navbar-light bg-faded">
<button class="navbar-toggler navbar-toggler-right" 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>
<a class="navbar-brand" href="#">My App</a>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mr-auto">
<li class="nav-item active">
<a class="nav-link" href="#home">Home <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Features</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Download</a>
</li>
</ul>
<form class="form-inline my-2 my-lg-0">
<input class="form-control mr-sm-2" type="text" placeholder="Search">
<button class="btn btn-success my-2 my-sm-0" type="submit">Search</button>
</form>
</div>
</nav>
<div class="jumbotron bg">
<h1 class="display-3">My Amazing App!</h1>
<p class="lead">The MAIN reason for YOU to download THIS app on your handheld Android or iOS device.</p>
<hr class="my-4">
<p class="lead">Want to learn more ? Join our Mailing List and get a free bonus.</p>
<form class="form-inline justify-content-center">
<label class="sr-only" for="email">Email</label>
<div class="input-group mb-2 mr-sm-2 mb-sm-0">
<div class="input-group-addon">@</div>
<input style="width: 350px;" type="email" class="form-control solid-gray-border" id="email" placeholder="Your Email">
</div>
<button type="submit" class="btn btn-primary">Sign Up</button>
</form>
</div>