CSS 질문드려요 채택완료

#container {width:100%; height:100vh; float:left; overflow:hidden; min-height:800px}
#container:after {display:block;visibility:hidden;clear:both;content:""}
#container .member {position:absolute; left:0; top:0; width:730px; height:100%}
#container .member .login {width:100%; padding:0 100px;}
#container .member ul {height:100%;}
#container .member li {float:left; line-height:60px}
#container .member li:first-child {width:20%}
#container .member li:last-child {width:70%}
#container .member li p {font-size:22px; color:#0e0e0e; font-weight:500}

login 클래스가 자식들의 높이에 맞게 정해져야하는데 왜 높이가 0으로 나오죠?

login에 position을 쓴것도 아닌데요... 

<div id="container">
    <div class="member">
        <div class="login">
            <ul>
                <li><p>아이디</p></li>
                <li><input type="text" id="wr_id" name="wr_id" class="full_ip" required placeholder="아이디를 입력해 주세요"></li>
            </ul>
        </div>

        <div class="login">
            <ul>
                <li><p>비밀번호</p></li>
                <li><input type="text" id="wr_name" name="wr_name" class="full_ip" required placeholder="비밀번호를 입력해 주세요"></li>
            </ul>
        </div>
    </div>

</div>