问无法使用引导程序在打印页的同一行中显示3列

EN

<div class="container main">
<div class="main_inner">
    <div class="row" >
          <div class="col-md-12" >
        <div class="col-md-3">
            <img src="../img/logo.jpg">
        </div>
        <div class="col-md-6">

            <h2>
                <center><b><?php echo   $row['municipality_address'];?> नगरपालिका</b></center>
            </h2>
            <h3>
                <center><b>नगरकार्यपालिकाको कार्यालय</b></center>
            </h3>
        </div>
        <div class="col-md-3">
            <div class="border_box"></div>
        </div>
    </div>
        <b></b>
    </div>

.main{
margin-top: 10px;
border: 5px solid #00bfff;
}
.main_inner{
margin: 50px;
margin-top: 150px;
margin-bottom: 80px;
}