字段文本过渡动画效果

 效果展示

代码实现：

*{
            margin:0;
            padding:0;
            box-sizing: border-box;
            font-family: 'Poppins', sans-serif;
        }
        body{
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            flex-direction: column;
            gap:30px;/*设置网格行的间隙30px,x,y间隙都为30px*/
            background: #b1d7ff;
        }
        .inputBox{
            position:relative;
            width:250px;
        }
        .inputBox input{
            width:100%;
            padding:10px;
            border:1px solid rgba(255,255,255,0.25);
            background: #b1d7ff;
            border-radius: 5px;
            outline: none;
            color: #ffffff;
            font-size: 1em;
            transition: .5s;

        }
        .inputBox span{
            position:absolute;
            left:0;
            padding:10px;
            pointer-events:none;/*指针属性：该元素永远不会成为鼠标事件的 target*/
            font-size: 1em;
            color:rgba(255,255,255,0.25);
            text-transform:uppercase; 
            transition: .5s;
        }
        .inputBox:nth-child(2) input:valid ~ span,
        .inputBox:nth-child(2) input:focus ~ span{
            background: #df9800;
            color:#b1d7ff;
        }
        .inputBox input:valid ~ span,/*让位于input元素之后的所有span元素设置写入文本框有效值时候触发*/
        .inputBox input:focus ~ span{
            color:#df9800;
            transform:translateX(10px) translateY(-7px);
            font-size:.65em;
            padding:0 10px;
            background: #b1d7ff;
            border-left: 1px solid #df9800;
            border-right: 1px solid #df9800;
            letter-spacing:0.2em;
        }
        .inputBox input:valid,/*写入文本框有效值时候触发*/
        .inputBox input:focus{ 
            border: 1px solid #df9800; 
        }

    <div class="inputBox">
        <input type="text" required="required">
        <span>First Name</span>
    </div>
    
    <div class="inputBox">
        <input type="text" required="required">
        <span>Last Name</span>
    </div>