【CSS 布局】水平垂直方向居中

单行元素

<div class="container"><div class="item"></div>
</div>

• 方式一：relative 和 absolute

.container {position: relative;height: 400px;border: 1px solid #ccc;.item {position: absolute;width: 200px;height: 200px;left: 0;right: 0;bottom: 0;top: 0;margin: auto;border: 1px solid #ccc;}
}

• 方式二：relative 和 absolute（变种，适合于宽高固定）

.container {position: relative;height: 400px;border: 1px solid #ccc;.item {position: absolute;top: 50%;left: 50%;margin-top: -100px;margin-bottom: -100px;width: 200px;height: 200px;border: 1px solid #ccc;}
}

• 方式三：flex 和 margin

.container {display: flex;height: 400px;border: 1px solid #ccc;.item {width: 300px;height: 300px;border: 1px solid #ccc;margin: auto; /* 关键点 */ }
}

• 方式四：flex

.container {display: flex;height: 400px;border: 1px solid #ccc;justify-content: center;align-items: center;.item {width: 300px;height: 300px;border: 1px solid #ccc;}
}

• 方式五：flex

.container {display: flex;height: 400px;border: 1px solid #ccc;justify-content: center;.item {width: 300px;height: 300px;border: 1px solid #ccc;align-self: center;}
}

多行元素

<div class="container"><img src="./login.png" alt="" /><p>欢迎访问我的个人博客 hhmax.xyz</p><button>按钮</button>
</div>

.container {height: 400px;border: 1px solid #ccc;display: flex;justify-content: center;flex-direction: column;align-items: center;
}