* {
    margin: 0;
    padding: 0;
}

ul,
ol {
    list-style: none;
}

a {
    text-decoration: none;
}

body {
    font: normal 14px/25px '微软雅黑';
}

header {
    height: 80px;
    background-color: #07cbc9;
}

header .mainHeader {
    width: 1200px;
    height: 80px;
    margin: 0 auto;
}

header .mainHeader .logo {
    float: left;
    height: 48px;
    margin: 16px 0;
}

header .mainHeader .mainNav {
    float: right;

}


header .mainHeader .mainNav ul li {
    float: left;
    color: white;
    font-size: 16px;
    text-align: center;
    line-height: 80px;
    margin-right: 20px;
}

header .mainHeader .mainNav ul li a{
    font-size: 16px;
    display: block;
    color: white;
}

header .mainHeader .mainNav ul li a:hover{
    background-color: orange;
}

HEML部分

​<header>
        <div class="mainHeader">
            <!-- logo -->
            <div class="logo">
                <img src="./images/logo.png" alt="">
            </div>

            <!-- 导航 -->
            <nav class="mainNav">
                <ul>
                    <li><a href="">HOME</a></li>
                    <li><a href="">ABOUT</a></li>
                    <li><a href="">GALLERY</a></li>
                    <li><a href="">FACULTY</a></li>
                    <li><a href="">EVENTS</a></li>
                    <li><a href="">CONTACT</a></li>
                </ul>
            </nav>
        </div>
    </header>

有一个问题是，li用margin向右踹，想给a:hover设置背景颜色，中间会有间隔，比较难看。怎么能让背景颜色连在一起