You have to set position 'relative' with z-index and set drop down absolute position. Updated css is below:
#menu-outer {
height: 41px;
background: rgba(0, 0, 0, 0.6);
margin-bottom:10px;
border:2px solid black;
z-index: 1;
position:relative; /*Set this property*/
}
.header{
display: table;
margin: 0 auto;
padding-top:1px;
}
body{
background: url("images/background.jpeg") no-repeat;
background-attachment: fixed;
}
ul{
margin: 0px;
padding: 0px;
list-style: none;
font-family: georgia;
font-size:20px;
}
ul li{
float: left;
width: 250px;
height: 50px;
line-height: 40px;
text-align: center;
}
ul li a{
text-decoration: none;
color: white;
display: block;
}
ul li a:hover{
background: rgba(0, 0, 0, 1);
color:white;
}
ul li ul li{
display: none;
}
ul li:hover ul li{
display: block;
background: rgba(0, 0, 0, 0.6);
color:white;
}
ul li ul li:hover{
text-decoration:underline;
color:white;
}
/*Add this code also*/
.header ul li ul{
position:absolute;
top: 43px;
}
.main{
height:2000px;
width:1400px;
background-color:white;
display: table;
margin: 0 auto;
margin-top:80px;
padding-top:30px;
padding-left:30px;
}
.meme{
padding-bottom: 30%;
height: 0;
width:30%;
margin:1%;
float:left;
display:block;
}
Modified fiddle code link is below.
https://jsfiddle.net/39ux9Lmz/
を設定することができます