实现material文本框效果

1.效果

https://supperjoy-1318445645.cos.ap-chengdu.myqcloud.com/blog/lejian-front%20-%20%E4%B8%AA%E4%BA%BA%20-%20Microsoft%E2%80%8B%20Edge%202024-01-07%2010-39-42.mp4

2.实现代码

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<div class="box">
        <div class="login-box">
            <h1 style="color: #FC6C37; text-align: center;">One Key Run</h1>
            <div class="form-item">
                <div class="input">
                    <input required id="username" type="text">
                    <span class="bar"></span>
                    <label for="username">手机号</label>
                    <img src="../assets/user.svg" alt="">
                </div>
                <div class="input">
                    <input required id="password" type="password">
                    <span class="bar"></span>
                    <label for="username">密码</label>
                    <img src="../assets/password.svg" alt="">
                </div>
                <div class="btn">
                    登录
                </div>
            </div>
        </div>
    </div>

<style lang='less' scoped>
.box {
    width: 100%;
    height: 100%;
    position: relative;
}

.login-box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 500px;
    height: 400px;
    // background-color: #bfc;
    border-radius: 10px;
}

.form-item {
    position: absolute;
    width: 80%;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    margin: auto;

    input {
        box-sizing: border-box;
        width: 100%;
        height: 40px;
        border: none;
        outline: none;
        padding: 5px;
        background-color: transparent;
        color: #FC6C37;
        font-weight: 700;
        font-size: 16px;
        border-bottom: 2px solid grey;
        padding-left: 40px;
    }

    input:valid~label,
    input:focus~.bar {
        width: 100%;
    }
    input:valid~label,
    input:focus~label {
        transform: translate(-30px,-45px);
        color: #FC6C37;
        font-weight: bold;
    }
    .input{
        position: relative;
        margin-top: 40px;
    }
    label {
        position: absolute;
        top: 50%;
        left: 35px;
        transform: translateY(-50%);
        font-size: 16px;
        color: grey;
        transition: all 0.3s;
    }
    .bar {
        position: absolute;
        bottom: 0;
        left: 0;
        width: 0;
        height: 2px;
        background-color: #FC6C37;
        // transform: scaleX(0);
        transition: all 0.2s ease-in-out;
    }
    .btn{
        width: 100%;
        background-color: #FC6C37;
        border-radius: 10px;
        height: 40px;
        text-align: center;
        line-height: 40px;
        color: #fff;
        margin-top: 30px;
        cursor: pointer;
    }
    img{
        position: absolute;
        top: 0;
        left: 0;
        width: 30px;
    }
}
</style>

3.关键

使用浏览器自带的判断文本框是否为空来控制动画

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<input required id="username" type="text">
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input:valid~label,

  input:focus~label {

    transform: translate(-30px,-45px);

    color: #FC6C37;

    font-weight: bold;

  }