.content,
header,
main {
    width: 100%;
}
.dropdown li,
.sidebar ul {
    list-style-type: none;
}
.dropdown button,
.nav-btn {
    font-family: auto;
    color: #fff;
    cursor: pointer;
}
#nextVideoBtn,
.book-btn,
.close-button,
.exit-btn,
.nav-btn,
.round-button,
.subject-btn {
    cursor: pointer;
}
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
::-webkit-scrollbar {
    width: 5px;
}
::-webkit-scrollbar-track {
    box-shadow: inset 0 0 5px grey;
    border-radius: 30px;
}
::-webkit-scrollbar-thumb {
    background: #d8935b;
    border-radius: 30px;
    padding: 20px;
}
::-webkit-scrollbar-thumb:hover {
    background: #b30000;
}
body {
    font-family: Arial, sans-serif;
    border-radius: 1px;
    background-image: url(../img/background.jpg);
    background-size: 100%;
}
.container {
    display: flex;
    flex-direction: row;
    padding: 3px;
    justify-content: space-between;
    flex-wrap: wrap;
    align-items: flex-start;
}
header {
    padding: 3px;
    border-radius: 13px;
    border: 0 solid red;
    border-bottom: 0px solid #00000085;
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    flex-direction: row;
    justify-content: space-evenly;
}
.exit-btn {
    background-color: #111657;
    color: #fff;
    border: none;
    border-radius: 10px;
}
.sidebar,
main {
    background-color: #ffe2e200;
}
.content {
    display: flex;
    flex-wrap: nowrap;
    padding: 40px;
    justify-content: space-between;
    align-items: flex-start;
}
.book-btn,
.dropdown,
.sidebar,
.subject-btn {
    display: block;
}
main {
    margin: 0px;
    border: 0px solid #ffffff;
    padding: 0px;
    background: #faebd700;
    border-radius: 16px;
    position: relative;
}
.sidebar {
    width: 24%;
    padding: 5px;
    border-radius: 16px;
    height: 600px;
    background: rgb(203 199 199 / 8%);
    overflow: auto;
    backdrop-filter: blur(3px);
    color: #fff;
    margin: 6px;
    scroll-behavior: smooth;
    border: 1px solid #4e8adf33;
}
.sidebar h2 {
    margin-bottom: 17px;
    position: static;
    text-align: center;
    padding: 19px;
    background-image: url(../img/button3.png);
    background-size: 100% 100%;
    border: 0px solid #fff;
    color: #0e3967;
    font-weight: 900;
    border-radius: 10px;
    text-shadow: 2px 2px 2px #0000006e;
}
.subject-btn {
    width: 100%;
    padding: 14px;
    color: #fff;
    box-shadow: 3px 2px 2px 0 #ffffff61;
    border-radius: 10px;
    transition: 0.3s ease-in-out;
    background-color: #110e4d;
    margin-bottom: 10px;
    border: 0 ridge #edededf7;
}
.subject-btn:hover {
    background-color: #1c20af;
    border-radius: 19px;
    color: #fff;
    font-size: 25px;
    box-shadow: inset 0 0 3px 0 #00000091;
}
.book-btn {
    padding: 15px;
    border-radius: 14px;
    transition: 0.5s ease-in-out, _ 0.5s ease-in-out;
    -webkit-transition: background-color 2s ease-out;
    -moz-transition: background-color 2s ease-out;
    -o-transition: background-color 2s ease-out;
    border: 1px ridge #edededf7;
    width: 88%;
    margin: auto auto 10px;
    font-weight: bold;
    color: #021932;
    background-color: #000;
    background-image: url("../img/button.png");
    background-size: 100% 100%;
    border: 0px ridge #edededf7;
}
.book-btn2 {
    padding: 30px;
    border-radius: 14px;
    transition: 0.5s ease-in-out, _ 0.5s ease-in-out;
    -webkit-transition: background-color 2s ease-out;
    -moz-transition: background-color 2s ease-out;
    -o-transition: background-color 2s ease-out;
    border: 0px ridge #edededf7;
    cursor: pointer;
    width: 16%;
    margin: auto auto 10px;
    text-shadow: 1px 1px 3px #00000057;
    color: #0e3967;
    font-weight: 900;
    background-image: url("../img/button2.png");
    background-size: 100% 100%;
    background-color: #fdfdfd00;
}
.dropdown,
.dropdown li {
    transition: max-height 0.6s ease-out, opacity 0.6s ease-out;
}
.book-btn:hover {
    transition: 0.3s ease-in-out;
    border-radius: 14px;
    padding-left: 15%;
    color: #000000;
    filter: invert(1); /* margin-left: 13%; */
    border-bottom: 0px solid #fff;
}
.book-btn2:hover {
    transition: 0.3s ease-in-out;
    border-radius: 14px;
    padding-left: 6%;
    color: #000000;
    filter: hue-rotate(123deg);
    border-bottom: 0px solid #fff;
}
.dropdown {
    max-height: 0;
    opacity: 0;
    overflow: hidden;
}
.dropdown.expanded {
    max-height: 3496px;
    opacity: 1;
}
.dropdown li {
    margin-bottom: 9px;
    margin-left: 5%;
    padding: 5px;
    border: 1px solid #00000045;
    background: #115dafba;
    border-radius: 25px;
    text-align: start;
    vertical-align: middle;
}
.dropdown button {
    background-color: #001f41;
    border: 0 solid;
    border-radius: 10px;
    display: flex;
    padding: 7px 17px;
    margin-left: 2%;
    box-shadow: 2px 2px 2px 0 #ffffff3b;
    transition: 0.4s ease-in-out;
    font-size: 20px;
    text-align: left;
    flex-direction: column;
    flex-wrap: wrap;
    justify-content: space-between;
}
.dropdown button:hover {
    background-color: #2a23af;
    margin-left: 7px;
}
.sidebar h2 {
    font-size: 31px;
}
.book-btn,
.subject-btn {
    text-align: left;
    font-size: 18px;
    padding-left: 11%;
    transition: 0.3s ease-in-out;
}

.book-btn2 {
    text-align: left;
    font-size: 20px;
    padding-left: 5.5%;
    transition: 0.3s ease-in-out;
}
.exit-btn,
.nav-btn {
    padding: 12px;
    font-size: 20px;
}
.next-video {
    margin-top: 10px;
}
#nextVideoBtn {
    font-size: 26px;
    background-color: #ff914d;
    border: none;
    padding: 12px;
    border-radius: 56%;
}
#nextVideoBtn:hover {
    background-color: #ff751a;
}
.nav-buttons {
    margin-top: 20px;
}
.nav-btn {
    padding: 9px 20px;
    text-shadow: 1px 2px 1px #000000ab;
    font-weight: bolder;
    font-size: 23px;
    background: #001f41;
    border: 0 ridge #edededf7;
    border-radius: 7px;
}
.nav-btn:hover {
    background-color: #0716af;
}
.video-container {
    position: relative;
    max-width: 1110px;
    margin: 0 auto;
    background: #ffffff8f;
    border-radius: 5px;
    padding: 0px;
    overflow: hidden;
}
.video-controls {
    display: flex;
    justify-content: space-around;
    align-items: center;
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    background: rgb(0 0 0 / 19%);
    padding: 5px;
    border-radius: 5px;
    opacity: 1;
    transition: opacity 0.6s;
}
.video-controls.hidden {
    opacity: 0;
}
.round-button {
    background: #fff;
    border: none;
    border-radius: 50%;
    width: 40px;
    height: 40px;
    display: flex;
    justify-content: center;
    align-items: center;
}
input[type="range"]#progressBar {
    flex: 1;
    margin: 0 10px;
}
#currentTime,
#totalTime {
    color: #fff;
    font-size: 14px;
    background-color: #0e5198;
    padding: 8px;
    border-radius: 5px;
}
.volume-control {
    display: flex;
    align-items: center;
    padding: 5px;
}
#pdfList,
.modal {
    display: none;
}
input[type="range"]#volumeControl {
    width: 70px;
    margin-left: 5px;
}
@media (max-width: 480px) {
    .sidebar h2 {
        font-size: 24px;
    }
    .book-btn,
    .subject-btn {
        font-size: 18px;
    }
    .exit-btn,
    .nav-btn {
        font-size: 20px;
    }
}
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    justify-content: center;
    align-items: center;
}
.modal-content {
    position: relative;
    background-color: #fff;
    padding: 7px;
    border-radius: 5px;
    width: 1340px;
    height: 780px;
}
.close-button {
    position: absolute;
    top: -19px;
    right: -29px;
    background-color: #040404;
    color: #fff;
    font-weight: 900;
    border: 2px solid #0000006e;
    border-radius: 5px;
    padding: 5px;
    font-size: 12px;
}
iframe {
    width: 100%;
    height: 100%;
    border: none;
}
.pdfbtn {
    width: 100%;
    background-color: #8b0000;
}