问两个容器需要是相同的size...and，但事实并非如此:为什么？

EN

@charset "utf-8";
/* CSS Document */

body {
    max-width: 890px;
    margin:auto;
}
.logo {
    font-size: 30px;
    font-family: Sylfaen;
    color: #FFF;
    text-align: left;
    padding-top: 30px;
    padding-left: 10px;
    padding-bottom: 100px;
    line-height: 0px;
    margin:auto;
    width:890px;
    height: 50%;
    background:url(header2.jpg) no-repeat;
    border-top-left-radius: 3%;
    border-top-right-radius: 3%;
}

.SUB {
    font-size: 18px;
    text-shadow:1px 1px #000
    padding-top: 30px;

}
.Titre {
    font-family: Downcome;
    -webkit-text-stroke: 1px black;
}

.main-menu ul {
    margin: 0;
    padding: 0px 0px;
    list-style: none;
}
.main-menu ul li {
    float: left;
    width: 296.6px;
    background-color: black;
    text-color: white;
    text-align: center;
    font-size: 20px;
}
.main-menu ul li a {
    text-decoration: none;
    color: white;
    display: block;
    text-transform: uppercase;
}

.main-menu ul li a:hover {
     text-decoration: underline;
     color: red;
}

ul li ul li{
    display: none;
    float: left;
    width: 296.6px;

}

ul li:hover ul li{
    display: block;
    max-height: 50%;
}

.content{
    margin:auto;
    width:100%;
    background:white;
    box-shadow: 5px 0px 5px 0px rgba(0, 0, 50, 0.97);
}