如何修复 css 中的解析错误 [:]

Question

这是与我在Web开发课上处理的作业相关的代码。W3C CSS 验证器不断给我以下消息："64 解析错误 [：]"。这是什么，我该如何解决？请帮忙！

这是我的 css：

*  {
    box-sizing: border-box;
}
body {
         background-color: #ffffff; 
         color: #666666;
         background-image: url(../images/background.jpg);
         font-family: Verdana, Arial, sans-serif;
}
#wrapper {
         background-color: #90c7e3;
         width: 80%; 
         min-width: 700px;
         max-width: 1024px;
         box-shadow: 10px 10px 5px #888888;
         margin-right: auto;
         margin-left: auto;
}
header {
         background-color: #000033;
         color: #ffffff;
         font-family: Georgia, "Times New Roman", serif;
}
h1 {
         background-image: url(../images/sunset.jpg);
         background-repeat: no-repeat;
         background-position: right; 
         padding-left: 20px;
         height: 72px; 
         line-height: 200%;
         margin-bottom: 0;
}
nav {
         float: left;
         width: 160px;
         padding-top: 20px;
         padding-right: 5px;
         padding-left: 20px;
         padding-bottom: 0;
         padding: 5px; 
         font-weight: bold;
}
nav a {
         text-decoration: none;
}
nav a:hover { 
     color: #ffffff;
}
nav a:link: {
    color: #000033;
}
nav a:visited {
    color: #344873;
}
nav ul {
    list-style-type: none;
    margin: 0;
    padding-left: 0;
}
main {
         background-color: #ffffff;
         margin-left: 170px;
         padding-top: 1px;
         padding-bottom: 1px;
         padding-left: 20px;
         padding-right: 20px;
         display: block; 
}
h2 {
         color: #3399cc;
         font-family: Georgia, "Times New Roman", serif;
}
h3 {
    color: #000033; 
}
dt {
         color: #000033;
         font-weight: bold;
}
.resort {
         color: #000033;
         font-size: 1.2em;
}

#homehero {
         background-image: url(../images/coast.jpg);
         height: 300px;
         background-size: 100% 100%;
         margin-right: 0;
         margin-left: 170px;
         background-repeat: no-repeat; 
}
#yurthero {
         background-image: url(../images/yurt.jpg);
         background-size: 100% 100%;
         background-repeat: no-repeat;
         height: 300px;
         margin-left: 170px;
}
#trailhero {
         background-image: url(../images/trail.jpg);
         height: 300px;
         background-size: 100% 100%;
         background-repeat: no-repeat;
         margin-left: 170px;
}

footer {
         background-color: #ffffff;
         margin-left: 170px;
         font-size: .70em;
         font-style: italic;
         text-align: center;
         padding: 10px; 
}
header, nav, main, footer {
     display: block;
}

Answer 1

这是因为nav a:link: {将其替换为nav a:link {