.login-box {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 400px;
    padding: 40px;
    transform: translate(-50%, -50%);
    background: rgba(24, 20, 20, 0.987);
    box-sizing: border-box;
    box-shadow: 0 15px 25px rgba(0,0,0,.6);
    border-radius: 10px;
}

    .login-box .user-box {
        position: relative;
    }

        .login-box .user-box input {
            width: 100%;
            padding: 10px 0;
            font-size: 16px;
            color: #fff;
            margin-bottom: 30px;
            border: none;
            border-bottom: 1px solid #fff;
            outline: none;
            background: transparent;
        }

        .login-box .user-box label {
            position: absolute;
            top: 0;
            left: 0;
            padding: 10px 0;
            font-size: 16px;
            color: #fff;
            pointer-events: none;
            transition: .5s;
        }

        .login-box .user-box input:focus ~ label,
        .login-box .user-box input:valid ~ label {
            top: -20px;
            left: 0;
            color: #bdb8b8;
            font-size: 12px;
        }

    .login-box form a {
        position: relative;
        display: inline-block;
        padding: 10px 20px;
        color: #ffffff;
        font-size: 16px;
        text-decoration: none;
        text-transform: uppercase;
        overflow: hidden;
        transition: .5s;
        margin-top: 40px;
        letter-spacing: 4px
    }

    .login-box a:hover {
        background: #03f40f;
        color: #fff;
        border-radius: 5px;
        box-shadow: 0 0 5px #03f40f, 0 0 25px #03f40f, 0 0 50px #03f40f, 0 0 100px #03f40f;
    }

    .login-box a span {
        position: absolute;
        display: block;
    }

@keyframes btn-anim1 {
    0% {
        left: -100%;
    }

    50%,100% {
        left: 100%;
    }
}

.login-box a span:nth-child(1) {
    bottom: 2px;
    left: -100%;
    width: 100%;
    height: 2px;
    background: linear-gradient(90deg, transparent, #03f40f);
    animation: btn-anim1 2s linear infinite;
}