/* ===== CSS Variables ===== */
:root {
    --primary-color: #c8102e;
    --secondary-color: #ffd700;
    --text-color: #333;
    --light-bg: #f5f5f5;
}

/* ===== Reset ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Arial, sans-serif;
}

body {
    color: var(--text-color);
    line-height: 1.6;
    padding-top: 80px;
    background-color: var(--light-bg);
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; 
}

/* === Header === */
header {
    background-color: var(--primary-color);
    color: white;
    padding: 10px 0;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 15px;
}

.logo img {
    height: 60px;
}

.logo-text h1 {
    font-size: 22px;
    font-weight: bold;
    line-height: 1.2;
    margin-bottom: 5px;
}

.logo-text p {
    font-size: 14px;
    font-weight: bold;
    color: var(--secondary-color);
    text-shadow: 0 1px 2px rgba(0,0,0,0.3);
}

/* === Navigation === */
nav {
    display: flex;
    align-items: center;
}

.main-menu {
    display: flex;
    list-style: none;
    align-items: center;
    margin: 0;
    padding: 0;
}

.main-menu > li {
    position: relative;
    margin-left: 20px;
}

.main-menu > li > a {
    color: white;
    text-decoration: none;
    font-weight: 600;
    font-size: 16px;
    transition: all 0.3s;
    padding: 8px 0;
    display: block;
    position: relative;
}

.main-menu > li > a:hover {
    color: var(--secondary-color);
}

.main-menu > li > a:after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    background: var(--secondary-color);
    bottom: 0;
    left: 0;
    transition: width 0.3s;
}

.main-menu > li > a:hover:after {
    width: 100%;
}

/* Dropdown menu */
.dropdown {
    position: relative;
    display: inline-block;
}

.dropdown-button {
    color: white;
    text-decoration: none;
    font-weight: 600;
    font-size: 16px;
    padding: 8px 0;
    display: block;
    cursor: pointer;
}

.dropdown-content {
    display: none;
    position: absolute;
    background: white;
    min-width: 200px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    z-index: 100;
    max-height: 400px;
    overflow-y: auto;
    border-radius: 5px;
}

.dropdown-content a {
    color: #333;
    padding: 10px 15px;
    text-decoration: none;
    display: block;
    border-bottom: 1px solid #eee;
    font-size: 14px;
}

.dropdown-content a:hover {
    background: #f0f0f0;
    color: var(--primary-color);
}

.dropdown:hover .dropdown-content {
    display: block;
}

.register-btn {
    background: white;
    color: var(--primary-color);
    padding: 8px 20px;
    border-radius: 30px;
    font-weight: bold;
    margin-left: 15px;
    transition: all 0.3s;
}

.register-btn:hover {
    background: #f0f0f0;
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

/* === Mobile Menu Toggle === */
.hamburger-btn {
    display: none;
    flex-direction: column;
    justify-content: space-between;
    width: 30px;
    height: 22px;
    background: transparent;
    border: none;
    cursor: pointer;
    z-index: 1001;
}

.hamburger-line {
    display: block;
    width: 100%;
    height: 3px;
    background: white;
    transition: all 0.3s;
}

/* === Multi-level Dropdown Menu === */
nav ul ul {
    position: absolute;
    top: 100%;
    left: 0;
    background: white;
    min-width: 200px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s;
    transform: translateY(10px);
    z-index: 100;
}

nav ul ul ul {
    left: 100%;
    top: 0;
}

nav ul li:hover > ul {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

nav ul ul li {
    margin: 0;
    border-bottom: 1px solid #eee;
    display: block !important;
    width: 100% !important;
    float: none !important;
}

nav ul ul li:last-child {
    border-bottom: none;
}

nav ul ul a {
    color: #333 !important;
    padding: 10px 15px !important;
    white-space: nowrap;
    display: block !important;
    width: 100% !important;
    float: none !important;
}

nav ul ul a:hover {
    background: #f6dd02 !important;
    color: #fff !important;
    padding-left: 20px !important;
}

nav ul ul ul li {
    display: block !important;
    width: 100% !important;
}

nav ul ul ul a {
    display: block !important;
    width: 100% !important;
}

nav ul ul .fa-chevron-right {
    float: right;
    font-size: 12px;
    margin-top: 5px;
}

/* === Slider === */
.slider {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    overflow: hidden;
    position: relative;
}

.slide {
    position: relative;
    width: 100%;
    height: 400px;
    background-size: cover;
    background-position: center;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
}

.slide-content {
    position: absolute;
    bottom: 50px;
    left: 10%;
    max-width: 500px;
    background: rgba(0,0,0,0.7);
    color: white;
    padding: 30px;
    text-align: center;
    border-radius: 10px;
    animation: slideIn 0.8s ease-out;
    z-index: 10;
}

.slide-content h2 {
    margin: 0 0 15px;
    font-size: 32px;
    color: var(--secondary-color);
}

.slide-content p {
    margin: 0 0 20px;
    font-size: 18px;
}

.share-btn {
    background: #3b5998;
    color: white;
    padding: 10px 20px;
    text-decoration: none;
    border-radius: 30px;
    font-weight: bold;
    margin: 0 5px;
    display: inline-block;
}

.register-btn:hover {
    background: #a50e26;
}

.share-btn:hover {
    background: #2a4373;
}

.slick-prev, .slick-next {
    font-size: 0;
    line-height: 0;
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    background: rgba(0,0,0,0.5);
    color: white;
    border: none;
    padding: 10px;
    cursor: pointer;
    z-index: 10;
}

.slick-prev {
    left: 10px;
}

.slick-next {
    right: 10px;
}

.slick-dots {
    text-align: center;
    padding: 10px 0;
}

.slick-dots li {
    display: inline-block;
    margin: 0 5px;
}

.slick-dots li button {
    font-size: 0;
    width: 10px;
    height: 10px;
    background: #ccc;
    border-radius: 50%;
    border: none;
    cursor: pointer;
}

.slick-dots li.slick-active button {
    background: var(--primary-color);
}

@keyframes slideIn {
    from { transform: translateY(50px); opacity: 0; }
    to { transform: translateY(0); opacity: 1; }
}

/* === News Section === */
.news-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 30px;
}

.news-item {
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    transition: all 0.3s;
    background: white;
}

.news-item:hover {
    transform: translateY(-10px);
    box-shadow: 0 15px 30px rgba(0,0,0,0.15);
}

.news-img {
    height: 200px;
    overflow: hidden;
}

.news-img img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.5s;
}

.news-item:hover .news-img img {
    transform: scale(1.1);
}

.news-content {
    padding: 20px;
}

.news-date {
    color: var(--primary-color);
    font-size: 14px;
    margin-bottom: 10px;
    font-weight: 500;
}

.news-content h3 {
    font-size: 18px;
    margin-bottom: 10px;
    color: #333;
}

.news-content p {
    color: #666;
    font-size: 15px;
}

/* === Features === */
.features {
    background: #f9f9f9;
    padding: 60px 0;
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 30px;
    text-align: center;
}

.feature-item {
    background: white;
    padding: 30px 20px;
    border-radius: 8px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.05);
    transition: all 0.3s;
}

.feature-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 25px rgba(0,0,0,0.1);
}

.feature-item i {
    font-size: 40px;
    color: var(--primary-color);
    margin-bottom: 20px;
}

.feature-item h3 {
    margin-bottom: 15px;
    color: #333;
}

.feature-item p {
    color: #666;
    font-size: 15px;
}

/* === Footer === */
footer {
    background: #1a1a1a;
    color: white;
    padding: 60px 0 20px;
}

.footer-container {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 40px;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

.footer-col h3 {
    font-size: 20px;
    margin-bottom: 20px;
    position: relative;
    padding-bottom: 10px;
    color: var(--secondary-color);
}

.footer-col h3:after {
    content: '';
    position: absolute;
    width: 50px;
    height: 2px;
    background: var(--primary-color);
    bottom: 0;
    left: 0;
}

.footer-col p {
    color: #bbb;
    font-size: 15px;
    line-height: 1.6;
}

.footer-col ul {
    list-style: none;
}

.footer-col ul li {
    margin-bottom: 10px;
}

.footer-col ul li a {
    color: #ddd;
    text-decoration: none;
    transition: all 0.3s;
    display: inline-block;
}

.footer-col ul li a:hover {
    color: var(--secondary-color);
    transform: translateX(5px);
}

.contact-info p {
    margin-bottom: 15px;
    display: flex;
    align-items: center;
    color: #ddd;
}

.contact-info i {
    margin-right: 10px;
    color: var(--primary-color);
    width: 20px;
    text-align: center;
}

.social-links a {
    display: inline-block;
    color: white;
    margin-right: 15px;
    font-size: 20px;
    transition: all 0.3s;
}

.social-links a:hover {
    color: var(--secondary-color);
    transform: translateY(-3px);
}

.copyright {
    text-align: center;
    padding-top: 30px;
    margin-top: 30px;
    border-top: 1px solid rgba(255,255,255,0.1);
    color: #bbb;
    font-size: 14px;
}

/* === Chatbox === */
.chat-icon {
    position: fixed;
    bottom: 20px;
    right: 20px;
    width: 60px;
    height: 60px;
    background-color: #10c875;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(0,0,0,0.2);
    z-index: 1000;
}

.chat-icon i {
    color: white;
    font-size: 24px;
}

.chat-box {
    position: fixed;
    bottom: 90px;
    right: 20px;
    width: 350px;
    height: 450px;
    background: white;
    border-radius: 10px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.2);
    z-index: 1001;
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.3s ease;
    display: none;
    flex-direction: column;
}

.chat-box.show {
    opacity: 1;
    transform: translateY(0);
    display: flex;
}

.chat-header {
    background: #6fc810;
    color: white;
    padding: 15px;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.chat-header h3 {
    margin: 0;
    font-size: 16px;
}

.close-chat {
    background: none;
    border: none;
    color: white;
    font-size: 20px;
    cursor: pointer;
}

.chat-content {
    flex: 1;
    padding: 15px;
    overflow-y: auto;
}

.chat-input {
    padding: 10px;
    border-top: 1px solid #eee;
    display: flex;
}

.chat-input input {
    flex: 1;
    padding: 8px;
    border: 1px solid #ddd;
    border-radius: 4px;
    margin-right: 10px;
}

.chat-input button {
    background: #f1ebec;
    color: white;
    border: none;
    padding: 8px 15px;
    border-radius: 4px;
    cursor: pointer;
}

/* === Responsive === */
@media (max-width: 992px) {
    .news-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .features-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 20px;
    }
    
    .footer-container {
        grid-template-columns: repeat(2, 1fr);
        gap: 30px;
    }
    
    nav ul li {
        margin-left: 12px;
    }
    
    nav ul li a {
        font-size: 14px;
        white-space: nowrap;
    }
    
    .register-btn {
        padding: 6px 12px;
        font-size: 14px;
    }
}

@media (max-width: 768px) {
    body {
        padding-top: 60px;
    }
    
    .header-container {
        align-items: center;
        height: 60px;
    }
    
    .hamburger-btn {
        display: flex;
        width: 24px;
        height: 18px;
    }
    
    nav {
        position: fixed;
        top: 60px;
        left: -50%;
        width: 50%;
        height: calc(100vh - 60px);
        background-color: var(--primary-color);
        transition: all 0.3s ease;
        z-index: 999;
        overflow-y: auto;
    }
    
    nav.active {
        left: 0;
    }
    
    nav ul {
        flex-direction: column;
        padding: 15px 0;
    }
    
    nav ul li {
        margin: 0;
        width: 100%;
        text-align: left;
        border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    }
    
    nav ul li a {
        padding: 10px 20px;
        font-size: 14px;
    }
    
    nav ul ul {
        position: static;
        display: none;
        background-color: rgba(0, 0, 0, 0.4);
        box-shadow: none;
        opacity: 1;
        visibility: visible;
        transform: none;
        width: 100%;
    }
    
    nav ul ul.active {
        display: block;
    }
    
    nav ul ul li {
        border-bottom: none;
    }
    
    nav ul ul a {
        padding: 8px 20px 8px 30px !important;
        font-size: 13px;
        word-break: break-word;
        color: var(--secondary-color) !important;
    }
    
    nav ul ul ul a {
        padding-left: 40px !important;
        font-size: 13px;
        word-break: break-word;
        color: var(--secondary-color) !important;
    }
    
    .register-btn {
        margin: 10px 20px;
        width: calc(100% - 40px);
        text-align: center;
        padding: 6px 15px;
        font-size: 14px;
    }
    
    .slide {
        height: 300px;
    }
    
    .slide-content {
        left: 5%;
        right: 5%;
        max-width: none;
        padding: 20px;
    }
    
    .slide-content h2 {
        font-size: 24px;
    }
    
    .slide-content p {
        font-size: 16px;
    }
    
    .news-grid,
    .features-grid,
    .footer-container {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .logo {
        flex-direction: row;
        text-align: center;
    }
    
    .logo img {
        margin-bottom: 10px;
    }
    
    .slide-content h2 {
        font-size: 24px;
    }
    
    .slide-content {
        bottom: 30px;
        padding: 20px;
    }
}

.hamburger-btn.active .hamburger-line:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}
.hamburger-btn.active .hamburger-line:nth-child(2) {
    opacity: 0;
}
.hamburger-btn.active .hamburger-line:nth-child(3) {
    transform: rotate(-45deg) translate(7px, -7px);
}

/* === Zalo Button (ưu tiên code sau) === */
.official-zalo-btn {
    position: fixed;
    bottom: 25px;
    left: 25px;
    width: 60px;
    height: 60px;
    background-color: #0068ff;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 20px rgba(0, 104, 255, 0.3);
    z-index: 9999;
    cursor: pointer;
    transition: all 0.3s;
    animation: zaloPulse 2s infinite;
}

.official-zalo-btn:hover {
    transform: scale(1.1);
}

.official-zalo-btn img {
    width: 34px;
    height: 34px;
    pointer-events: none;
}

/* Popup chức năng */
.zalo-actions {
    position: fixed;
    bottom: 100px;
    left: 25px;
    width: 200px;
    background: white;
    border-radius: 12px;
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.15);
    z-index: 9998;
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.3s;
    visibility: hidden;
    padding: 15px;
}

.zalo-actions.show {
    opacity: 1;
    transform: translateY(0);
    visibility: visible;
}

.zalo-action {
    display: flex;
    align-items: center;
    padding: 10px 12px;
    margin-bottom: 8px;
    border-radius: 8px;
    color: #333;
    text-decoration: none;
    font-weight: 500;
    transition: all 0.2s;
}

.zalo-action:hover {
    background: #f0f7ff;
}

.zalo-action img {
    width: 24px;
    height: 24px;
    margin-right: 10px;
}

/* Animation */
@keyframes zaloPulse {
    0% { box-shadow: 0 0 0 0 rgba(0, 104, 255, 0.5); }
    70% { box-shadow: 0 0 0 15px rgba(0, 104, 255, 0); }
    100% { box-shadow: 0 0 0 0 rgba(0, 104, 255, 0); }
}

/* === Bản đồ === */
.map-link {
    color: #ddd;
    text-decoration: none;
    transition: all 0.3s;
    border-bottom: 1px dashed var(--secondary-color);
    padding-bottom: 1px;
}

.map-link:hover {
    color: var(--secondary-color);
    border-bottom-color: transparent;
}

.contact-info .fa-map-marker-alt {
    color: var(--secondary-color);
    margin-right: 8px;
}

.main-content {
    width: 100%;
    background: white;
    border-radius: 5px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    padding: 30px;
    overflow-wrap: break-word;
    word-wrap: break-word;
}

.article-title {
    color: var(--primary-color);
    font-size: 28px;
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--secondary-color);
    text-align: center;
}

.doc-subtitle {
    color: #555;
    font-size: 18px;
    margin-bottom: 15px;
    text-align: center;
}

.doc-meta {
    display: flex;
    justify-content: center;
    gap: 20px;
    color: #666;
    font-size: 14px;
    flex-wrap: wrap;
    margin-bottom: 30px;
}

.doc-meta i {
    color: var(--primary-color);
    margin-right: 5px;
}

.article-subtitle {
    color: var(--primary-color);
    font-size: 22px;
    padding-bottom: 8px;
    border-bottom: 1px dashed #ccc;
    margin: 30px 0 15px;
    display: flex;
    align-items: center;
}

.article-subtitle i {
    margin-right: 10px;
    font-size: 20px;
}

canvas {
    border: 1px solid #000;
    max-width: 100%;
    height: auto;
}

.drawing-tools button {
    touch-action: manipulation;
    min-width: 60px;
    min-height: 60px;
    font-size: 1.2rem;
    margin: 5px;
}

.nav-menu {
    display: flex;
    gap: 1rem;
}

#menu-toggle {
    display: none;
}

@media (max-width: 640px) {
    .nav-menu {
        display: none;
        flex-direction: column;
        position: absolute;
        top: 60px;
        left: 0;
        right: 0;
        background: #1e3a8a;
        padding: 1rem;
    }
    .nav-menu.active {
        display: flex;
    }
    #menu-toggle {
        display: block;
        font-size: 1.5rem;
        background: none;
        border: none;
        color: white;
    }
}

.summary-box {
    background-color: #0b3a2e;
    color: #ffffff;
    padding: 15px;
    border-radius: 10px;
    margin-bottom: 15px;
    border-left: 5px solid #ef4444;
}

.options {
    margin: 10px 0;
}

.option {
    margin: 5px 0;
}

.answer-check {
    margin-top: 10px;
}

.answer-check button {
    padding: 12px 24px;
    background: #ef0909;
    color: white;
    border: none;
    border-radius: 25px;
    cursor: pointer;
    transition: background 0.3s;
}

.answer-check button:hover {
    background: #d10808;
}

.answer-feedback {
    margin-top: 10px;
    font-weight: bold;
}

.correct {
    color: #22c55e;
}

.incorrect {
    color: #ef4444;
}

.solution {
    background-color: #0b3a2e;
    color: #f0ebea;
    font-family: 'Courier New', 'Segoe Script', cursive;
    padding: 15px;
    margin-top: 15px;
    border-radius: 8px;
    border: 1px solid #0a2e23;
    box-shadow: 2px 2px 8px rgba(0,0,0,0.4);
    display: none;
}

.solution.visible {
    display: block;
    color: rgb(241, 243, 241);
}

.solution-toggle {
    margin-left: 10px;
    padding: 4px 10px;
    cursor: pointer;
    background-color: #0b3a2e;
    color: white;
    border: 1px solid white;
    border-radius: 4px;
}

.solution-toggle:hover {
    background-color: #145a47;
}

.hot {
    color: #ef4444;
    font-weight: bold;
}

img {
    max-width: 100%;
    height: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin: 15px 0;
}

table, th, td {
    border: 1px solid #ddd;
    padding: 10px;
    text-align: center;
}

th {
    background: #6b21a8;
    color: white;
}

.navigation {
    display: flex;
    justify-content: space-between;
    margin: 20px 0;
}

.navigation button {
    padding: 12px 24px;
    background: #6b21a8;
    color: white;
    border: none;
    border-radius: 25px;
    cursor: pointer;
    transition: background 0.3s;
}

.navigation button:hover {
    background: #5b1a8b;
}

.navigation button:disabled {
    background: #9ca3af;
    cursor: not-allowed;
}

@media (max-width: 640px) {
    h1 { font-size: 1.6rem; }
    h2 { font-size: 1.6rem; }
    h3 { font-size: 1.3rem; }
    .card { padding: 15px; }
    .header .logo { font-size: 1.4rem; }
    .nav-bar { top: 50px; flex-direction: column; align-items: flex-start; }
    .nav-bar a { font-size: 0.9rem; margin-right: 10px; }
    .dropdown-button { font-size: 0.9rem; padding: 6px 12px; }
    .dropdown-content { min-width: 80px; }
    table { font-size: 0.85rem; }
    .answer-check button, .navigation button {
        padding: 8px 16px;
        font-size: 0.9rem;
    }
}

.score-section {
    background-color: #ecfdf5;
    padding: 20px;
    border-radius: 10px;
    margin-bottom: 20px;
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.1);
    text-align: center;
}

#score-result {
    margin-top: 10px;
    font-weight: bold;
}

#score-result.correct {
    color: #22c55e;
}

#score-result.incorrect {
    color: #ef4444;
}

.question img, .solution img {
    display: block;
    margin: 5px auto;
    width: 300px;
    height: 200px;
    object-fit: contain;
    object-position: center;
    background: #0b3a2e;
}

.question img.long-image, .solution img.long-image {
    height: auto;
    max-width: 100%;
}

.question img:not([src]), .solution img:not([src]),
.question img[src=''], .solution img[src=''],
.question img[onerror], .solution img[onerror] {
    display: none !important;
}

@media (max-width: 640px) {
    .question img, .solution img {
        max-width: 100%;
        width: auto;
        height: auto;
        margin: 2px auto;
    }
    .question img.long-image, .solution img.long-image {
        max-width: 100%;
        height: auto;
    }
}

.latex-solution {
    background-color: rgba(0, 0, 0, 0.4);
    color: white;
    font-family: Courier New, monospace;
    font-size: 18px;
    border-radius: 6px;
    padding: 6px;
}



/* Modal Đăng Nhập */
#login-modal {
    z-index: 50;
}

#login-modal .bg-white {
    background-color: #ffffff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.1);
    max-width: 400px;
    width: 90%;
}

#login-modal input {
    width: 100%;
    padding: 10px;
    margin-bottom: 16px;
    border: 2px solid #ccc;
    border-radius: 5px;
    font-size: 16px;
}

#login-modal button {
    padding: 12px 24px;
    border: none;
    border-radius: 25px;
    cursor: pointer;
    font-size: 16px;
}

#login-modal button[type="submit"] {
    background: #6b21a8;
    color: white;
}

#login-modal button[type="submit"]:hover {
    background: #5b1a8b;
}

#login-modal button#close-modal {
    background: #6b7280;
    color: white;
}

#login-modal button#close-modal:hover {
    background: #4b5563;
}

#auth-status {
    margin-top: 10px;
    font-weight: bold;
}

@media (max-width: 640px) {
    #login-modal .bg-white {
        width: 95%;
        padding: 15px;
    }
    #login-modal input, #login-modal button {
        font-size: 14px;
        padding: 8px 16px;
    }
}


/* Canvas vẽ */
#drawCanvas {
    position: fixed;          /* luôn cố định trên màn hình */
    top: 0;                   /* dính sát mép trên */
    left: 0;                  /* dính sát mép trái */
    z-index: 9970;            /* nằm dưới toolbar (toolbar có z-index cao hơn) */
    /*pointer-events: auto; /* cho phép vẽ */
    touch-action: none;       /* tắt thao tác chạm mặc định (để vẽ trên mobile) */
}
#drawCanvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  display: none;          /* Ẩn mặc định */
  z-index: 9970;          /* chỉ phủ khi bật vẽ */
  touch-action: none;
}

/* Khi bật chế độ vẽ */
body.draw-mode #drawCanvas { display: block; }

/* ==================== Canvas vẽ ==================== */


/* ==================== Thanh công cụ vẽ ==================== */
.toolbar {
  position: fixed;
  top: 80px; left: 8px;
  width: 50px;
  background: rgba(255,255,255,0.95);
  border: 1px solid #ccc;
  border-radius: 8px;
  padding: 8px 4px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
  display: none;            /* Ẩn mặc định */
  flex-direction: column;
  align-items: center;
  gap: 6px;
  z-index: 9980;
}

/* Khi bật chế độ vẽ */
body.draw-mode #drawCanvas { display: block; }
body.draw-mode .toolbar { display: flex; }

/* Nút công cụ trong thanh dọc */
.toolbar .drawing-tools button,
.toolbar button {
  width: 36px;
  height: 36px;
  min-width: 36px;
  min-height: 36px;
  margin: 4px 0;
  font-size: 20px;
  padding: 0;
  background: #f0f0f0;
  border: 1px solid #bbb;
  border-radius: 6px;
  cursor: pointer;
}

.toolbar button:hover {
  background: #e0e0e0;
}

/* Chọn công cụ */
.toolbar #tool {
  width: 36px;
  height: 36px;
  padding: 0;
}

/* Bộ chọn màu */
#colorPicker {
  width: 36px;
  height: 36px;
  border: none;
  padding: 0;
  cursor: pointer;
}

/* Điều chỉnh nét bút (thanh trượt dọc) */
#draw-width {
  width: 36px;
  height: 120px;
  writing-mode: bt-lr;
  -webkit-appearance: slider-vertical;
}


/* Nút nổi góc phải dưới */
.floating-button {
    position: fixed;          /* cố định */
    bottom: 20px;             /* cách mép dưới 20px */
    right: 20px;              /* cách mép phải 20px */
    z-index: 10001;           /* nổi hơn canvas & toolbar */
    background: #ec0c1e;      /* màu đỏ */
    color: white;             /* chữ trắng */
    border: none;             /* bỏ viền */
    padding: 12px 20px;       /* khoảng trong nút */
    border-radius: 50px;      /* bo tròn kiểu pill */
    font-size: 16px;          /* chữ lớn vừa */
    cursor: pointer;          /* hiện con trỏ tay */
    box-shadow: 0 4px 8px rgba(0,0,0,0.2); /* bóng */
}

/* Nút bật/tắt bảng (góc trái dưới) */
.blackboard-toggle {
    position: fixed;          /* cố định */
    bottom: 20px;             /* cách đáy 20px */
    left: 10px;               /* cách trái 10px */
    z-index: 10020;           /* nổi cao hơn mọi thứ */
    background: #c0153c;      /* nền đỏ đậm */
    color: white;             /* chữ trắng */
    border: none;             /* bỏ viền */
    width: 32px;              /* rộng nút */
    height: 32px;             /* cao nút */
    font-size: 18px;          /* cỡ chữ/icon */
    line-height: 32px;        /* căn giữa dọc */
    text-align: center;       /* căn giữa ngang */
    border-radius: 50%;       /* bo tròn tròn */
    cursor: pointer;          /* con trỏ tay */
    box-shadow: 0 2px 4px rgba(0,0,0,0.2); /* bóng nhỏ */
    display: block !important; /* luôn hiển thị */
}

.blackboard-toggle:hover, 
.blackboard-toggle.active {
    background: #a50e26;      /* đổi màu khi hover hoặc active */
}

/* Blackboard */
.blackboard {
    position: fixed;          /* cố định giữa màn */
    top: 50%;                 /* căn giữa dọc */
    left: 50%;                /* căn giữa ngang */
    transform: translate(-50%, -50%); /* dịch để đúng giữa */
    width: 80vw;              /* rộng 80% viewport */
    height: 60vh;             /* cao 60% viewport */
    max-width: 800px;         /* tối đa 800px */
    max-height: 600px;        /* tối đa 600px */
    background: #004d00;      /* nền xanh đậm */
    border: 5px solid #8B4513;/* viền nâu */
    border-radius: 10px;      /* bo tròn */
    z-index: 9960;            /* dưới toolbar */
    display: none;            /* ẩn mặc định */
    cursor: move;             /* hiển thị icon di chuyển */
}

.blackboard.show {
    display: block !important; /* ép hiển thị khi có class show */
}

/* Nút đóng bảng */
#close-blackboard {
    position: absolute;       /* nằm trong blackboard */
    top: 10px;                /* cách trên 10px */
    right: 10px;              /* cách phải 10px */
    background: #c0153c;      /* đỏ */
    color: white;             /* trắng */
    border: none;             /* bỏ viền */
    padding: 5px 10px;        /* đệm trong */
    border-radius: 50%;       /* nút tròn */
    cursor: pointer;          /* con trỏ tay */
    z-index: 10001;           /* nổi cao trong blackboard */
}

#close-blackboard:hover {
    background: #a50e26;      /* đỏ đậm hơn khi hover */
}

/* Responsive */
@media (max-width: 768px) {
    .blackboard {
        width: 90vw;          /* bảng nhỏ hơn trên mobile */
        height: 50vh;
        max-width: 400px;
        max-height: 300px;
    }
    .blackboard-toggle {
        width: 28px;          /* thu nhỏ nút */
        height: 28px;
        font-size: 16px;
        line-height: 28px;
        bottom: 10px;         /* cách mép nhỏ hơn */
        left: 5px;
    }
    .toolbar {
        width: 40px;          /* toolbar hẹp hơn trên mobile */
        top: 80px;
        left: 5px;
    }
    .floating-button {
        bottom: 10px;
        right: 10px;
        padding: 8px 16px;
        font-size: 14px;
    }
}
.fullscreen-mode {
  font-size: 1.4em;   /* tăng toàn bộ chữ lên 1.4 lần */
  line-height: 1.6;
}

.fullscreen-mode h1 {
  font-size: 2.2em;
}
.fullscreen-mode h2 {
  font-size: 1.8em;
}