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所以我正在開發一個網站使用引導4，一切工作正常，但我有列，需要自動浮動，但它沒有，是否有任何問題與引導4或我錯過了什麼， 因爲這可以解決太寫作自定義CSS，但我認爲我失去了一些東西，請幫助。引導4網格系統不會自動浮動
<?php
include ("layouts/header.php");
?>
<section class="booking">
<div class="container">
<div class="row">
<div class="section-header">
<h2>Booking Procedures</h2>
</div>
<div class="section-content">
<div class="col-12">
<form>
<div class="card text-center">
<div class="card-header">
Booking Step 2 Of 2
</div>
<div class="card-block">
<p>All * fields are compulsory</p>
<div class="col-12 col-md-3">
<div class="form-group">
<select class="form-control">
<option>Title</option>
<option>Mr.</option>
<option>Mrs.</option>
<option>Miss</option>
</select>
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="First Name *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Middle Name" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Last Name *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<select class="form-control" required="required">
<option>Nationality</option>
<option>Chinese</option>
<option>Indian</option>
</select>
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control datepicker" placeholder="Date Of Birth *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Occupation" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="email" class="form-control" placeholder="Email Address *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Detail Mailing Address *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Mobile Number *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Landline" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Passport Number *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control" placeholder="Place Of Issue *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control datepicker" placeholder="Date Of Issue *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<input type="text" class="form-control datepicker" placeholder="Date Of Expiry *" />
</div>
</div>
<div class="col-12 col-md-3">
<div class="form-group">
<select class="form-control" required="required">
<option>How did you find us</option>
<option>Friends</option>
<option>Family</option>
<option>Online</option>
<option>Travel Blog</option>
<option>Trip Advisor</option>
<option>Others</option>
</select>
</div>
</div>
<div class="col-12">
<div class="form-group">
<textarea class="form-control" placeholder="Emergency Contact * "></textarea>
</div>
</div>
</div>
<div class="col-12">
<p>Note: Please kindly note that you should be covered for, I- medical expenses, II- emergency air ambulance & III- Trip cancellation to plan this trip.</p>
</div>
<div class="col-12">
<div class="form-group">
<button type="submit" class="btn btn-sample3">Submit</button>
</div>
</div>
</div>
</form>
</div>
</div>
</div>
</div>
</section>
<?php include("layouts/footer.php"); ?>
結果，我想 
結果我得到 
你知道BS4 **不使用浮動* *...對？ –
是嗎？我需要正確閱讀文檔...我的不好 – designerdarpan
BS4基於Flexbox。 –