导入Bootstrap样式表时图像消失

我的网站上有一个页面，当我将鼠标悬停在其中一张图片上时，会出现一个带有图像标题的覆盖。以下是其中一个图像的代码:

<div id="content">
            <div class="mosaic-block fade">
                <a target ="_blank" href = "files/file1.pdf" class="mosaic-overlay">
                    <div class="details">
                        <h4>Form #1</h4>
                        <p>Permission Slip</p>
                        </div>
                </a>
                <div class="mosaic-backdrop"><img src="img/thumb1.jpg"/></div>
            </div>

这些样式表/脚本链接在我的标题，图像和覆盖工作

    <link rel="stylesheet" href="css/mosaic.css" type="text/css" media="screen" />
    <link rel="stylesheet" href="../events/eventInfoStyle.css" type="text/css" media="screen" />
    <link rel="stylesheet" type="text/css" href="../events/headbar.css">
    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.0/jquery.min.js"></script>
    <script type="text/javascript" src="../events/header.js"></script>
    <script type="text/javascript" src="js/mosaic.1.0.1.js"></script>

但是当我添加bootstrap时，图像不再出现。以下是我正在添加的bootstrap。

<!-- Latest compiled and minified CSS -->
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
    <!-- jQuery library -->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
    <!-- Latest compiled JavaScript -->
    <script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

是什么导致图像不显示与Bootstrap添加?下面是我剩下的CSS:

MAIN.CSS:

    .nav{
  background-color:white;
 }
.affix{
  top: 0;
  width: 100%;
  margin-bottom:10px;
}
.nav a {
  color: #5a5a5a;
  font-size: 11px;
  font-weight: bold;
  padding: 14px 10px;
  text-transform: uppercase;

}
.nav li {
  display: inline;
}
.jumbotron {
  margin-top:5px;
  height: 700px;
  background-repeat: no-repeat;
  background-size: cover;
  background-color: #56A0D3;
  background-image: url('wvlogo.png');
}
.jumbotron .container {
  position: relative;
  top:100px;
}
.jumbotron h1 {
  color: #fff;
  font-size: 48px;  
  font-family: 'Shift', sans-serif;
  font-weight: bold;
  text-align:center;

}
.jumbotron p {
  font-size: 20px;
  color: #fff;
}
.learn-more {
  background-color: #f7f7f7;
}
.learn-more h3 {
  font-family: 'Shift', sans-serif;
  font-size: 18px;
  font-weight: bold;
}
.learn-more a {
  color: #00b0ff;
}
.announcements{
    background-color:#efefef;
    border-bottom: 1px solid #dbdbdb;
}
.announcements h2{
    color:#393c3d;
    font-size:24px;
    }
.announcements p{
    font-size:15px;
    color:rgb(0, 32, 96);
    margin-bottom:13px;
    text-align:center;
    height:150px;
    padding:30px;
    border-radius:25px;
    background-color: #56A0D3;
}

.myStatsLogin{
  background-color:#56A0D3;
  border-style:solid;
  border-width:5px;
  border-radius:25px;
  width:300px;
  text-align:center;
  margin:auto;
  color: rgb(0,32,96);
  font-size: 16px;
  font-weight: bold;
  padding: 7px 5px;
  text-transform: uppercase;
}
.carousel-announcement{
  height:200px;
  color:rgb(0,32,96);
  font-size:32px;
  background-color:#56A0D3;
  text-align:center;
  padding-top:20px;  
  padding-left:100px;
  padding-right:100px;
}
.section-title h1{
  font-size:48px;
  margin:0px;
  text-align:center;
  text-decoration:underline;
  color: rgb(0,32,96);
  background-color:#56A0D3;
}
EVENTINFOSTYLE.CSS:
h1{

    color:#002060;
     font-size: 40px;
      font-weight: bold;
      padding: 7px 5px;
      text-transform: uppercase;
      background-color:#56A0D3;
      border-radius:25px;
      border:solid 3px rgb(0,32,96);
    margin:0;
    margin-top:1em;
}

form{
    width:50%;
    position:relative;
    display:inline-block;
}
body{
    background-color:#00007f;
     background: linear-gradient(#B4D8E7, #00005f);
     /*background-repeat:no-repeat;
     height:100%;*/
     text-align:center;
}
.sideImage{
    float:right;
    width:40%;
    display:inline-block;
}
img{
    position:relative;
    width:100%;
}
.announcment{
    margin: 0 auto;
    background-color: rgba(0,32,96,.85);
    border-radius:15px;
    padding: 2em;
    display: block;
    position: relative;
    text-align: left;
}
.announcment h1{
    color: white;
    font-family: "Calisto MT", "Bookman Old Style", Bookman, "Goudy Old Style", Garamond, "Hoefler Text", "Bitstream Charter", Georgia, serif;
    font-style: italic;
    font-size: 3em;
    text-shadow:2px 2px #000;
    margin-top: 0;
    text-align: center;
}
.announcment h2{
    color: white;
    font-family: Candara, Calibri, Segoe, "Segoe UI", Optima, Arial, sans-serif;
    font-size: x-large;
    text-shadow:2px 2px #000;
}
.announcment p{
    color: white;
    font-family: Candara, Calibri, Segoe, "Segoe UI", Optima, Arial, sans-serif;
    font-size: large;
    text-shadow:2px 2px #000;
}

.announcment li{
    color: white;
    font-family: Candara, Calibri, Segoe, "Segoe UI", Optima, Arial, sans-serif;
    font-size: large;
    text-shadow:2px 2px #000;
}
.announcmentWrapper{
    margin: 0 auto;
    margin-bottom:2em;
    margin-top:2em;
    padding: 1em;
    width: 70%;
    background-color: #56A0D3;
    border-radius:25px ;
    position: relative;
    display: inline-block;
}

hr.experiencehr {
    border: 0;
    height: 1px;
    background: #3498db;
    background-image: -webkit-linear-gradient(left, rgba(0,50,96,.85), #3498db, rgba(0,50,96,.85)); 
    background-image:    -moz-linear-gradient(left, rgba(0,50,96,.85), #3498db, rgba(0,50,96,.85)); 
    background-image:     -ms-linear-gradient(left, rgba(0,50,96,.85), #3498db, rgba(0,50,96,.85)); 
    background-image:      -o-linear-gradient(left, rgba(0,50,96,.85), #3498db, rgba(0,50,96,.85)); 
}
li{
    line-height: 0em;
}
a:link{
    color:#eee;
}
a:visited{
    color:#ccc;
}
HEADBAR.CSS:
.signup{
    position:relative;
    border-left:1px solid black;
    color:white;
    float:right;
    padding: 0.5em;
    margin:0.2em;
    font-family: Candara, Calibri, Segoe, "Segoe UI", Optima, Arial, sans-serif;
    cursor:pointer;
    z-index:100;
}
.headbar{
    position:fixed;
    background:-o-linear-gradient(bottom, #005fbf 5%, #003f7f 100%);    background:-webkit-gradient( linear, left top, left bottom, color-stop(0.05, #005fbf), color-stop(1, #003f7f) );
    background:-moz-linear-gradient( center top, #005fbf 5%, #003f7f 100% );
    filter:progid:DXImageTransform.Microsoft.gradient(startColorstr="#005fbf", endColorstr="#003f7f");  background: -o-linear-gradient(top,#005fbf,003f7f);
    width:100%;
    z-index:9999;
    overflow:hidden;
    height:2.5em;
}
body{
    margin:0;
}