CSS(Cascading Style Sheets,层叠样式表)是一种用于描述HTML或XML(包括SVG、MathML等各种XML方言)文档样式的样式表语言。它让网页的呈现更加美观、布局更加合理,同时也提高了代码的可维护性。
CSS通过选择器(Selectors)来指定要应用样式的HTML元素,然后使用属性(Properties)和值(Values)来定义这些元素的样式。例如:
/* 选择器:选择所有的h1元素 */
h1 {
/* 属性:设置文本颜色 */
color: blue;
/* 属性:设置字体大小 */
font-size: 24px;
}
style
属性定义样式。<head>
部分使用<style>
标签定义样式。<link>
标签引用该文件。以下是一个简单的CSS示例,展示了如何使用CSS实现一个响应式导航栏:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Responsive Navbar</title>
<style>
body {
margin: 0;
font-family: Arial, sans-serif;
}
.navbar {
background-color: #333;
overflow: hidden;
}
.navbar a {
float: left;
display: block;
color: white;
text-align: center;
padding: 14px 20px;
text-decoration: none;
}
.navbar a:hover {
background-color: #ddd;
color: black;
}
.dropdown {
float: left;
overflow: hidden;
}
.dropdown .dropbtn {
font-size: 16px;
border: none;
outline: none;
color: white;
padding: 14px 20px;
background-color: inherit;
font-family: inherit;
margin: 0;
}
.navbar a:hover, .dropdown:hover .dropbtn {
background-color: red;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
}
.dropdown-content a {
float: none;
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
text-align: left;
}
.dropdown-content a:hover {
background-color: #ddd;
}
.dropdown:hover .dropdown-content {
display: block;
}
@media screen and (max-width: 600px) {
.navbar a, .dropdown .dropbtn {
float: none;
display: none;
}
.navbar a.icon {
float: left;
display: block;
}
}
@media screen and (max-width: 600px) {
.navbar.responsive {position: relative;}
.navbar.responsive a.icon {
position: absolute;
right: 0;
top: 0;
}
.navbar.responsive a {
float: none;
display: block;
text-align: left;
}
.navbar.responsive .dropdown {float: none;}
.navbar.responsive .dropdown-content {position: relative;}
.navbar.responsive .dropdown .dropbtn {
display: block;
width: 100%;
text-align: left;
}
}
</style>
</head>
<body>
<div class="navbar" id="myNavbar">
<a href="#home">Home</a>
<a href="#services">Services</a>
<div class="dropdown">
<button class="dropbtn">Dropdown
<i class="fa fa-caret-down"></i>
</button>
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
<a href="#">Link 3</a>
</div>
</div>
<a href="javascript:void(0);" class="icon" onclick="myFunction()">☰</a>
</div>
<script>
function myFunction() {
var x = document.getElementById("myNavbar");
if (x.className === "navbar") {
x.className += " responsive";
} else {
x.className = "navbar";
}
}
</script>
</body>
</html>
希望以上信息能够帮助您更好地理解CSS及其相关应用。
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