CSS 焦点
CSS 中的 ：focus 伪类表示已获得焦点的元素。此类通常在用户单击、点击元素或使用键盘的 Tab 键选择元素时触发。
：focus 伪类应用于 focussed 元素本身。要选择包含聚焦元素的元素，请使用 ：focus-within 伪类。
适用于
所有 HTML 元素，例如按钮、下拉列表、输入字段等。
语法
selector:focus{ properties }
CSS focus - 链接
下面是一个将焦点设置在链接上的示例：
<html>
<head>
<style>
a {
color: darkviolet;
transition: all 0.3s ease;
}
a:focus {
outline: none;
color: red;
background-color: yellow;
}
body {
margin: 5px;
padding: 2rem;
display: grid;
font: 20px/1.4 system-ui, -apple-system, sans-serif;
}
</style>
</head>
<body>
<p>Click on the link or press the tab key.</p>
<p>The link here has a <a href="#0">change in background and foreground color</a> as it is focussed.</p>
</body>
</html>
CSS focus - 按钮
下面是一个将焦点设置在按钮上的示例：
<html>
<head>
<style>
button {
display: block;
margin: 2em;
padding: 2px;
font-weight: bold;
font-size: 18px;
text-align: center;
color: black;
background-color: #fff;
border: 2px solid black;
border-radius: 24px;
cursor: pointer;
transition: all 0.3s ease;
width: 150px;
height: 50px;
}
button:hover {
color: blue;
border-color: black;
background-color: lightpink;
}
button:focus {
background-color: darkred;
color: white;
border-radius: 2px;
}
</style>
</head>
<body>
<p>Click on the button or press the tab key.</p>
<button>Click Me!!</button>
</body>
</html>
CSS focus - 输入框
以下示例将焦点设置在输入上：
<html>
<head>
<style>
label {
display: block;
font-size: 20px;
color: black;
width: 500px;
}
input[type="text"] {
padding: 10px 16px;
font-size: 16px;
color: black;
background-color: #fff;
border: 1px solid #597183;
border-radius: 8px;
margin-top: 5px;
width: 500px;
transition: all 0.3s ease;
}
input[type="text"]:focus {
background-color: lightyellow;
}
</style>
</head>
<body>
<p>Click on the text box or press the tab key.</p>
<form>
<label>
Full Name
<input type="text">
</label>
</form>
</body>
</html>
CSS focus - 下拉框
以下示例将焦点设置在下拉列表上：
<html>
<head>
<style>
label {
display: block;
font-size: 18px;
color: black;
width: 500px;
}
select {
padding: 10px 16px;
font-size: 16px;
color: black;
background-color: #fff;
border: 1px solid #597183;
border-radius: 8px;
margin-top: 25px;
width: 300px;
transition: all 0.3s ease;
}
select:focus {
background-color: rgb(173, 233, 209);
box-shadow: 20px 15px 30px yellow, -20px 15px 30px lime, -20px -15px 30px blue, 20px -15px 30px red;
}
</style>
</head>
<body>
<p>Select an item from the dropdown box.</p>
<form>
<label>
Ice cream Flavors:
<select name="flavor">
<option>Cookie dough</option>
<option>Pistachio</option>
<option>Cookies & Cream</option>
<option>Cotton Candy</option>
<option>Lemon & Raspberry Sorbet</option>
</select>
</label>
</form>
</body>
</html>
CSS focus- 切换按钮
以下示例将焦点设置在切换开关上：
<html>
<head>
<style>
.toggle {
position: relative;
display: block;
width: 100%;
margin: 2em;
}
.toggle label {
padding-right: 8px;
font-family: Verdana, Geneva, Tahoma, sans-serif;
font-size: 16px;
line-height: 28px;
color: black;
}
.toggle span {
position: relative;
display: inline-block;
vertical-align: middle;
cursor: pointer;
}
.toggle span:before {
display: block;
width: 50px;
height: 30px;
content: "";
background-color: #a9adaf;
border-radius: 28px;
transition: background-color 0.3s ease;
}
.toggle span:after {
position: absolute;
top: 1px;
left: 1px;
display: block;
width: 30px;
height: 28px;
visibility: visible;
content: "";
background-color: #fff;
border-radius: 28px;
transition: left 0.3s ease;
}
input[type="checkbox"]:checked ~ span:before {
background-color: orange;
}
input[type="checkbox"]:checked ~ span:after {
top: 1px;
left: 21px;
}
input[type="checkbox"]:hover ~ span:before {
background-color: #1194d1;
}
input[type="checkbox"]:not(:checked):hover ~ span:before {
background-color: #afbec9;
}
input[type="checkbox"]:focus ~ span:before {
outline: none;
box-shadow: 0 0 0 4px red;
}
</style>
</head>
<body>
<div class="toggle">
<label for="toggle1">Check the box to toggle me</label>
<input type="checkbox" id="toggle1" />
<span></span>
</div>
</body>
</html>
CSS focus - 关联属性
除了 ：focus 之外，还有两个伪类与 ：focus 伪类相关联。它们列在下表中：
| sr.no | 伪类 | 描述 |
|---|---|---|
| 1 | :focus-visible | 焦点明显地集中在元素上，并显示给用户。 |
| 2 | :focus-within | 将焦点设置在包含聚焦元素的元素上。 |
