*{
    margin: 0;
    padding: 0;

    list-style: none;
    text-decoration: none;
    font-family: "Roboto", sans-serif;
}

.background {

    position:
        absolute;

    display:
        block;

    top: 0;

    left: 0;

    z-index: -1;
}
body{
    margin: 0;

    padding: 0;
    /* 设置窗口的高度为100%的窗口高度 */
    height: 100vh;
    /* 伸缩盒子模型 */
    display: flex;
    /* 下面两个属性让body里的子类居中 */
    justify-content: center;
    align-items: center;
    background-color: #2c3e50;
}
.container{
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    width: 600px;
    height: 650px;
    border-radius: 20px;
    background-color: #34495e;
    box-shadow: 15px 15px 10px rgba(33,45,58,0.3);
    overflow: hidden;
    position: relative;
}
.container form{
    width: 600px;
    height: 600px;
    display: flex;
    justify-content: space-around;
    flex-direction: column;
    align-items: center;
    z-index: 1;
}
.tbx{
    width: 400px;
    height: 40px;
    outline: none;
    border: none;
    border-bottom: 1px solid #fff;
    background:none;
    color: #fff;
}
/* 设置placeholder */
.tbx::placeholder{
    color: #fff;
    font-size: 15px;
}
.sub{
    width: 200px;
    height: 40px;
    outline: none;
    border: 1px solid #fff;
    border-radius: 20px;
    letter-spacing: 5px;
    color: #fff;
    background: none;
    cursor: pointer;
}
.container h1{
    z-index: 1;
    color: #ecf0f1;
    letter-spacing: 5px;
    padding-left: 5px;
    font-size: 30px;
    font-weight: 100;
    text-shadow: 5px 5px 5px rgba(33,45,58,0.3);
}


/* 侧边栏 */
.sidebar{
    position: fixed;
    left: -250px;
    width: 250px;
    height: 100%;
    background: #042331;
    transition: all .5s ease;
}

.sidebar header{
    font-size: 22px;
    color: white;
    text-align: center;
    line-height: 70px;
    background: #063146;
    user-select: none;
}

.sidebar ul a{
    display: block;
    /* height: 100%;
    width: 100%; */
    line-height: 65px;
    font-size: 20px;
    color: white;
    padding-left: 40px;
    box-sizing: border-box;
    border-top: 1px solid rgba(255,255,255,.1);
    border-bottom: 1px solid black;
    transition: .4s;
}

ul li:hover a{
    padding-left: 50px;
}

.sidebar ul a i{
    margin-right: 16px;
}


#check{
    display: none;
}

label #btn,label #cancel{
    position: absolute;
    cursor: pointer;
    background: #042331;
    border-radius: 3px;
}

label #btn{
    left: 40px;
    top: 25px;
    font-size: 35px;
    color: white;
    padding: 6px 12px;
    transition: all .5s;
}

label #cancel{
    z-index: 1;
    left: -195px;
    top: 17px;
    font-size:30px;
    color: #0a5275;
    padding: 4px 9px;
    transition: all .5s ease;
}

#check:checked ~ .sidebar{
    left: 0;
}

#check:checked ~ label #btn{
    left: 250px;
    opacity: 0;
    pointer-events: none;
}

#check:checked ~ label #cancel{
    left: 195px;
}

#check:checked ~ section{
    margin-left: 250px;
}

.section{
    /* background: url(bg.png) no-repeat; */
    background-position: center;
    background-size: cover;
    height: 100vh;
    transition: all .5s;
}