css - 为什么我的 Bootstrap 列居中而不是左对齐？

Question

我正在使用标准的 Bootstrap 3 CSS。

我的问题图片:

我的 HTML 如下:

<div class="col-sm-12 col-lg-6 col-lg-offset-3 relative text-center">
    <h3 class="text-center">Tell Us More About Yourself:</h3>
    <label for="motto" class="col-sm-4 control-label">Motto:</label>
    <div class="col-sm-8">
        <input id="motto" type="text" class="form-control" name="motto" ng-model="profile.UserParams.Motto">
    </div>
    </br>
    </br>
    <label for="occupation" class="col-sm-4 control-label">Occupation:</label>
    <div class="col-sm-8">
        <input id="occupation" type="text" class="form-control" name="occupation" ng-model="profile.UserParams.Occupation">
    </div>
    </br>
    </br>
    <label for="location" class="col-sm-4 control-label">Location:</label>
    <div class="col-sm-8">
        <input id="location" type="text" class="form-control" name="location" ng-model="profile.UserParams.Location">
    </div>
    </br>
    </br>
    <button style="margin-top:25px;" class="btn btn-lg btn-primary" ng-click="updateProfile()">Update Profile</button>
</div>
<div style="margin-top:50px;" class="col-sm-12 col-lg-6 col-lg-offset-3 relative text-center">
    <h3>Change Your Password:</h3>
    <div class="form-group">
        <form name="changePassword">
            <label for="password" class="col-sm-4 control-label">New Password (must be at least 5 characters long):</label>
            <div class="col-sm-8">
                <input id="password" type="password" class="form-control" name="password" ng-minlength="5" ng-model="user.password" required>
            </div>
            </br>
            </br>
            <label for="cpassword" class="col-sm-4 control-label">Confirm New Password:</label>
            <div class="col-sm-8">
                <input id="cpassword1" type="password" class="form-control" name="cpassword" ng-minlength="5" ng-model="user.confirmPassword" compare-to="user.password" required>
                <div ng-messages="changePassword.cpassword.$error" style="color:maroon" role="alert">
                    <div ng-message="compareTo">Your passwords must match!</div>
                    <div ng-message="minlength">Your password is too short!</div>
                </div>
            </div>
            </br>
            </br>
            <button style="margin-top:25px;" class="btn btn-lg btn-danger" ng-click="changePasswordFunction()">Change Password</button>
        </form>
    </div>
    </br>
    </br>
</div>

我希望 <form>在 HTML 中镜像上面的 HTML/CSS(告诉我们更多关于你自己的信息)，但我得到了 Confirm New Password标签卡在中心，即使它应该 float:left;并在 New Password 下标签。该表单没有任何特殊的 CSS。为什么是Confirm New Password当它是一个 col-sm-4 时像那样居中？

我当前的视口(viewport)是一台达到 lg 的笔记本电脑断点，但奇怪的是，这个错误只出现在 768px 和大约 1600px 之间。当我使用 Chrome Dev Tools 设置宽桌面视口(viewport)时，我得到了正确的格式......但我不明白为什么要给我断点。

Answer 1

您面临 float 问题，因为您没有将元素包装在 .row 中，正如您在这个问题中看到的那样:Floated elements of variable height push siblings down

如果您不使用 Bootstrap 提供的容器/行，那么这就是您所拥有的:

div {
  border: 1px solid;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">

<div class="col-xs-4">
  lorem ipsum lorem ipsum lorem ipsum lorem ipsum lorem ipsum
</div>
<div class="col-xs-8">
  lorem ipsum lorem ipsum lore
</div>
<div class="col-xs-4">
  lorem ipsum lorem ipsum lorem ipsu
</div>
<div class="col-xs-8">
  lorem ipsum lorem ipsum lorem ipsum lorem ipsum lorem ipsum
</div>

如果您按照 Bootstrap 规则正确构建元素，您将获得:

div {
  border: 1px solid;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">

<div class="container">
  <div class="row">
    <div class="col-xs-4">
      lorem ipsum lorem ipsum lorem ipsum lorem ipsum lorem ipsum
    </div>
    <div class="col-xs-8">
      lorem ipsum lorem ipsum lore
    </div>
  </div>
  <div class="row">
    <div class="col-xs-4">
      lorem ipsum lorem ipsum lorem ipsu
    </div>
    <div class="col-xs-8">
      lorem ipsum lorem ipsum lorem ipsum lorem ipsum lorem ipsum
    </div>
  </div>