改變了我的div的寬度，現在中心不見了

Question

我已經添加了一個綠色背景色的div。我減少了寬度，因爲我不想覆蓋整個寬度。

但現在div正在向左對齊！

網址：http://185.123.96.102/~kidsdrum/moneynest.co.uk/

HTML

<div class="jumbotron"> 
    <div class="container text-center"> 
    <div class="h1extrapadding hidden-xs hidden-sm"></div> <h1 class="boldme">Aged 20-30 & frustrated with money?</h1> 
    <div class="greenpromobox"> 
    <div class="h2extrapadding hidden-xs hidden-sm"></div> <h2 class="boldme">Take our free <b class="jumpstarttext">Jumpstart Your Finances</b> class to<br /> quickly gain control over your finances</h2> 
    <p class="text-center"> 
       <br> 
      <!-- Begin MailChimp Signup Form --> 
<div id="mc_embed_signup"> 
<form action="//moneynest.us11.list-manage.com/subscribe/post?u=9ccf2d2219536b32eaae3c3d1&amp;id=299de51b4e" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate> 
    <div id="mc_embed_signup_scroll"> 


        <img src="http://185.123.96.102/~kidsdrum/moneynest.co.uk/img/hand-drawn-arrow.png" id="handarrow" class="hidden-xs hidden-sm" alt="arrow"><input type="email" value="" name="EMAIL" class="email" id="mce-EMAIL" placeholder="Enter your email address" required autofocus> 
    <!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups--> 
    <div style="position: absolute; left: -5000px;" aria-hidden="true"><input type="text" name="b_9ccf2d2219536b32eaae3c3d1_299de51b4e" tabindex="-1" value=""></div> 
    <div class="clear"><input type="submit" value="Start Class Now" name="subscribe" id="mc-embedded-subscribe" class="text-uppercase btn btn-primary btn-lg"></div> 
    </div> 
</form> 
</div> 

<!--End mc_embed_signup--> 

</div> 
</div> 

</div> 
</div> 

CSS

.greenpromobox { 
background-color: green; 
padding-top: 1px; 
margin-top:25px; 
    width: 70%; 
    border-radius: 5px; 
    text-align: center; 
} 

Answer 1

您減少寬度，那麼你需要保證金左和利潤率右自動

70％

.greenpromobox { 
     background-color: green; 
     padding-top: 1px; 
     margin-top:25px; 
     margin-left: auto; 
     margin-right: auto; 
     width: 70%; 
     border-radius: 5px; 
     text-align: center; 
} 

Answer 2

使用margin: auto;從左對齊&正確。