如何將圖像置於引導中心

如何居中放置此圖像以使其居中。我打算將按鈕放在圖像中，然後將它們放在容器的中心。但是，如果我嘗試修復它，菜單會繼續與綠色橫幅一起使用。這裏是我的HTML和CSS代碼至今： HTML如何將圖像置於引導中心

<div id="difficultyButton" class="col-lg-12 level mt" style="display:none; text-align:center;"> 
    <button type="button" class="myButton " id="btn_easy">Easy</button> 
    <br> 
    <button type="button" class="myButton " id="btn_medium">Medium</button> 
    <br> 
    <button type="button" class="myButton " id="btn_hard">Hard</button> 
    <br> 
    <button type="button" class="myButton mt " id="btn_exitStart">Exit</button> 
</div>

CSS

.level{ 
    height: 530px; 
    width: 600px; 
    -webkit-flex-wrap: wrap; 
    flex-wrap: wrap; 
    -webkit-align-content: center; 
    background-image: url("../images/CYL/levels.png"); 
    background-repeat: no-repeat; 
} 

myButton { 
    -moz-box-shadow:inset 0px 0px 0px 0px #3e7327; 
    -webkit-box-shadow:inset 0px 0px 0px 0px #3e7327; 
    box-shadow:inset 0px 0px 0px 0px #3e7327; 
    background: -moz-linear-gradient(top, #33a6cc 50%, #0099cc 50%); 
    background: -webkit-gradient(linear, left top, left bottom, color-stop(50%,#33a6cc), color-stop(50%,#0099cc)); 
    background: -webkit-linear-gradient(top, #33a6cc 50%,#0099cc 50%); 
    background: -o-linear-gradient(top, #33a6cc 50%,#0099cc 50%); 
    background: -ms-linear-gradient(top, #33a6cc 50%,#0099cc 50%); 
    background: linear-gradient(to bottom, #33a6cc 50%,#0099cc 50%); 
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#33a6cc', endColorstr='#0099cc',GradientType=0); 
    background-color:#FFFFFF; 
    -moz-border-radius:3px; 
    -webkit-border-radius:3px; 
    border-radius:3px; 
    display:inline-block; 
    cursor:pointer; 
    color:#ffffff; 
    width: 30%; 
    font-family:Arial; 
    font-size:19px; 
    padding:11px 76px; 
    text-decoration:none; 
    text-shadow:0px 0px 0px #5b8a3c; 
    margin-bottom: 10px 
}

這裏的東西現在的樣子：