* {
    margin: 0;
    padding: 0;
}

body {
    min-height: 100vh;
    /* 弹性布局 居中 */
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background-color: #6f8aa6;
}
.system-title {
    color: #cadff3; /* 使用比背景稍亮的浅蓝色 */
    font-weight: 700;
    margin-bottom: 50px;
    text-align: center;
    font-size: 2.5rem;
    /* 立体阴影 */
    text-shadow: 0 1px 0 #fff, /* 顶部高光 */
                 0 2px 0 #9cb2c9, /* 下方厚度感 */
                 0 3px 0 #9cb2c9,
                 0 4px 0 #9cb2c9,
                 0 5px 0 #89a1b9,
                 0 6px 1px rgba(0,0,0,0.1), /* 软阴影 */
                 0 0 5px rgba(0,0,0,0.1),
                 0 1px 3px rgba(0,0,0,0.3),
                 0 3px 5px rgba(0,0,0,0.2);
}

.container {
    background-color: #222;
    width: 350px;
    height: 550px;
    border-radius: 15px;
    overflow: hidden;
    position: relative;
}

.container::after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background: url("../images/bg.jpg") no-repeat;
    background-size: 500px;
    background-position: left bottom;
    opacity: 0.8;
}

/* 注册区域（登录区域很多样式和注册区域的一样，故而一些统一的样式写在了一起） */
.register-box {
    width: 70%;
    position: absolute;
    z-index: 1;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    transition: 0.3s ease;
}

.register-title,
.login-title {
    color: #fff;
    font-size: 27px;
    text-align: center;
}

.register-title span,
.login-title span {
    color: rgba(0, 0, 0, 0.4);
    display: none;
}

.register-box .input-box,
.login-box .input-box {
    background-color: #fff;
    border-radius: 15px;
    overflow: hidden;
    margin-top: 50px;
    opacity: 1;
    visibility: visible;
    transition: 0.6s ease;
}

.register-box input,
.login-box input {
    width: 100%;
    height: 30px;
    border: none;
    border-bottom: 1px solid rgba(0, 0, 0, 0.1);
    font-size: 12px;
    padding: 8px 0;
    text-indent: 15px;
    outline: none;
}

.register-box input:last-child,
.login-box input:last-child {
    border-bottom: none;
}

.register-box input::placeholder,
.login-box input::placeholder {
    color: rgba(0, 0, 0, 0.4);
}

.register-box button,
.login-box button {
    width: 100%;
    padding: 15px 45px;
    margin: 15px 0;
    background: rgba(0, 0, 0, 0.4);
    border: none;
    border-radius: 15px;
    color: rgba(255, 255, 255, 0.8);
    font-size: 13px;
    font-weight: bold;
    cursor: pointer;
    opacity: 1;
    visibility: visible;
    transition: 0.3s ease;
}

.register-box button:hover,
.login-box button:hover {
    background-color: rgba(0, 0, 0, 0.8);
}

/* 登录区域 */
.login-box {
    position: absolute;
    inset: 0;
    top: 20%;
    z-index: 2;
    background-color: #F0F8FF;
    transition: 0.3s ease;
}

.login-box::before {
    content: "";
    background-color: #fff;
    width: 200%;
    height: 250px;
    border-radius: 50%;
    position: absolute;
    top: -20px;
    left: 50%;
    transform: translateX(-50%);
}

.login-box .center {
    width: 70%;
    position: absolute;
    z-index: 3;
    left: 50%;
    top: 40%;
    transform: translate(-50%, -50%);
}

.login-title {
    color: #000;
}

.login-box .input-box {
    border: 1px solid rgba(0, 0, 0, 0.1);
}

.login-box button {
    background-color: #4A90E2;
}

/* 注册、登录区域收起 */
.login-box.slide-up {
    top: 90%;
}

.login-box.slide-up .center {
    top: 10%;
    transform: translate(-50%, 0%);
}

.login-box.slide-up .login-title,
.register-box.slide-up .register-title {
    font-size: 16px;
    cursor: pointer;
}

.login-box.slide-up .login-title span,
.register-box.slide-up .register-title span {
    margin-right: 5px;
    display: inline-block;
}

.login-box.slide-up .input-box,
.login-box.slide-up .button,
.register-box.slide-up .input-box,
.register-box.slide-up .button {
    opacity: 0;
    visibility: hidden;
}

.register-box.slide-up {
    top: 6%;
    transform: translate(-50%, 0%);
}