html,
body {
    margin: 0;
    padding: 0;
}

body {
    /*    font-family: sans-serif;
*/  font-family: Microsoft YaHei;
    font-size: 20px;
}

/* Style page content - use this if you want to push the page content to the right when you open the side navigation */
#app {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    width: 100vw;
    background-color: slategray;
    color: white;
    overflow-x: hidden; /* Disable horizontal scroll */
    overflow-y: hidden; /* Disable vertical scroll */
    transition: margin-left .5s;
    padding: 0;
}

.hide {
    display: none;
}

.background {
    z-index: 3; /* the stacking order of the element, with a higher value appearing on top of elements with lower values */
    position: relative; /* The element is positioned relative to its normal position */
    width: 100vw;
    height: 100vh;
    top: 0;
    right: 0;
}

/* The side navigation menu */
.sidenav {
    /*height: 100%;*/ /* 100% Full-height */
    height: 100vh; /* 100% Full-height */
    width: 0; /* 0 width - change this with JavaScript */
    position: fixed; /* Stay in place */
    z-index: 1; /* Stay on top */
    top: 0; /* Stay at the top */
    left: 0; /* Stay on the left */
    background-color: #111; /* Black*/
    overflow-x: hidden; /* Disable horizontal scroll */
    overflow-y: hidden; /* Disable vertical scroll */
    padding-top: 60px; /* Place content 60px from the top */
    transition: 0.5s; /* 0.5 second transition effect to slide in the sidenav */
}

    /* The navigation menu links */
    .sidenav a {
        padding: 8px 8px 8px 32px;
        text-decoration: none; /* Remove underline */
        font-size: 25px;
        color: #818181; /* Set the text color to grey */
        display: block; /* Make the links appear below each other */
        transition: 0.3s; /* Add a transition effect on hover */
    }

        /* When you mouse over the navigation links, change their color */
        .sidenav a:hover {
            color: #f1f1f1;
        }

    /* Position and style the close button (top right corner) */
    .sidenav .closebtn {
        position: absolute; 
        top: 0;
        right: 25px;
        font-size: 36px;
        margin-left: 50px;
    }

/* On smaller screens, where height is less than 450px, change the style of the sidenav (less padding and a smaller font size) */
@media screen and (max-height: 450px) {
    .sidenav {
        padding-top: 15px;
    }

        .sidenav a {
            font-size: 25px
        }
}