body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f4;
    background-image: url('hinh-nen-cay-xanh-2.png');
    background-size: cover;
    background-repeat: no-repeat;
    background-attachment: fixed;
    text-align: center;
}

/* Language Switcher Styles */
#language-switcher {
    position: absolute;
    top: 10px;
    right: 10px;
    z-index: 1000;
}

.dropdown {
    position: relative;
    display: inline-block;
}

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

.lang-btn {
    background-color: #fff;
    color: #333;
    padding: 4px 6px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 7px;
    font-weight: bold;
    transition: background-color 0.3s;
}

.lang-btn:hover {
    background-color: #e0e0e0;
}

.dropdown-content {
    display: none;
    position: absolute;
    right: 0;
    background-color: #fff;
    min-width: 160px;
    box-shadow: 0 8px 16px rgba(0,0,0,0.2);
    border-radius: 4px;
    z-index: 1001;
    margin-top: 4px;
}

.dropdown-content a {
    color: #333;
    padding: 10px 14px;
    text-decoration: none;
    display: block;
    font-size: 13px;
    transition: background-color 0.2s;
}

.dropdown-content a:hover {
    background-color: #f1f1f1;
}

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

/* End Language Switcher Styles */

header {
    background-color: #4CAF50;
    color: white;
    padding: 1em;
    margin: 0.1em 0;
    position: relative;
}

video {
    width: 80%;
    max-width: 600px;
    margin: 1em auto;
    display: block;
}

section {
    padding: 1em 2em 2em 2em;
    margin: 1em auto;
    max-width: 800px;
    background-color: rgba(46, 125, 50, 0.7);
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
    color: white;
}

.buttons {
    display: flex;
    justify-content: center;
    gap: 0.5em;
    margin-top: 19px;
}

.nav-buttons {
    display: flex;
    gap: 0.5em;
}

.button {
    background-color: #4CAF50;
    color: white;
    padding: 0.5em 1em;
    text-decoration: none;
    border-radius: 5px;
    transition: background-color 0.3s;
    flex: 1;
    text-align: center;
    white-space: nowrap;
}

.button:hover {
    background-color: #45a049;
}

.button.active {
    background-color: #66BB6A;
}

footer {
    text-align: center;
    padding: 1em;
    background-color: #333;
    color: white;
    margin-bottom: 80px; /* Space for mobile bottom nav */
}

/* Mobile Bottom Navigation */
.mobile-bottom-nav {
    display: none; /* Hidden by default on desktop */
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: #4CAF50;
    padding: 10px;
    z-index: 1000;
    box-shadow: 0 -2px 10px rgba(0,0,0,0.2);
}

.mobile-bottom-nav .nav-buttons {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.mobile-bottom-nav .button {
    background-color: rgba(255, 255, 255, 0.2);
    color: white;
    padding: 10px 15px;
    text-decoration: none;
    border-radius: 5px;
    font-size: 0.85em;
    text-align: center;
    transition: background-color 0.3s;
}

.mobile-bottom-nav .button:hover,
.mobile-bottom-nav .button.active {
    background-color: rgba(255, 255, 255, 0.4);
}

/* Show mobile bottom nav only on mobile (up to 600px) */
@media screen and (max-width: 600px) {
    .mobile-bottom-nav {
        display: block;
    }
    
    /* Hide original nav-buttons in header on mobile */
    header .nav-buttons {
        display: none;
    }
    
    /* Hide KALYNK_AN TUỆ text on mobile */
    header div:first-child {
        display: none;
    }
    
    /* Make section title larger (1.5x) */
    #kham-pha h2 {
        font-size: 1.5em !important;
    }
    
    #kham-pha small {
        font-size: 1.2em !important;
    }
    
    footer {
        margin-bottom: 70px;
    }
}

img {
    width: 100%;
    max-width: 250px;
    margin: 1em;
    border-radius: 8px;
}

.gallery {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.albums {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    justify-items: center;
}

.album {
    display: block;
    background: rgba(255, 255, 255, 0.1);
    padding: 20px;
    border-radius: 8px;
    text-decoration: none;
    color: white;
    text-align: center;
    min-width: 100px;
}

.album:hover {
    background: rgba(255, 255, 255, 0.2);
}

a.back {
    display: inline-block;
    margin-top: 1em;
    padding: 0.5em 1em;
    background-color: #4CAF50;
    color: white;
    text-decoration: none;
    border-radius: 5px;
}

a.back:hover {
    background-color: #45a049;
}

.mindmap {
    display: flex;
    color: white;
    align-items: center;
    position: relative;
}

.mindmap .root {
    padding: 15px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 8px;
    font-weight: bold;
    margin-right: 20px;
    position: relative;
}

.mindmap .root:after {
    content: '';
    position: absolute;
    right: -20px;
    top: 50%;
    width: 20px;
    height: 4px;
    background: white;
    transform: translateY(-50%);
}

.mindmap .branch {
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.mindmap .node {
    margin: 5px 0;
    padding: 10px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 8px;
    position: relative;
}

.mindmap .node:before {
    content: '';
    position: absolute;
    left: -40px;
    top: 50%;
    width: 40px;
    height: 4px;
    background: white;
    transform: translateY(-50%);
}

.mindmap .sub-branch {
    margin-left: 40px;
    display: flex;
    flex-direction: column;
}

.mindmap .sub-branch .node {
    background: rgba(255, 255, 255, 0.05);
}

.mindmap .sub-branch .node:before {
    content: '';
    position: absolute;
    left: -40px;
    top: 50%;
    width: 40px;
    height: 4px;
    background: white;
    transform: translateY(-50%);
}

.mindmap a {
    color: lightblue;
    text-decoration: none;
}

.mindmap a:hover {
    text-decoration: underline;
}

.flow-mindmap {
    display: flex;
    align-items: center;
    margin: 50px 0;
    color: white;
}

.flow-mindmap .center {
    background: rgba(255, 255, 255, 0.1);
    padding: 15px;
    border-radius: 8px;
    margin-right: 20px;
    font-weight: bold;
}

.flow-mindmap .branches {
    display: flex;
    flex-direction: column;
}

.flow-mindmap .branch {
    display: flex;
    align-items: center;
    margin: 5px 0;
}

.flow-mindmap .arrow {
    margin: 0 10px;
    font-size: 20px;
    color: white;
}

.flow-mindmap .node {
    background: rgba(255, 255, 255, 0.1);
    padding: 10px;
    border-radius: 8px;
    position: relative;
}

.flow-mindmap .sub-branches {
    margin-left: 20px;
    margin-top: 10px;
    display: flex;
    flex-direction: column;
}

.flow-mindmap .sub-branch {
    display: flex;
    align-items: center;
    margin: 5px 0;
}

.flow-mindmap a {
    color: yellow;
    text-decoration: none;
    font-size: 0.5em;
    font-weight: bold;
    text-shadow: 0 0 10px yellow;
}

.flow-mindmap a:hover {
    text-decoration: underline;
}

.radial-mindmap {
    text-align: center;
    margin: 50px auto;
    color: white;
}

.radial-mindmap .center {
    background: rgba(255, 255, 255, 0.1);
    padding: 20px;
    border-radius: 8px;
    display: inline-block;
    font-weight: bold;
    margin-bottom: 20px;
}

.radial-mindmap .branches {
    display: flex;
    justify-content: center;
    align-items: flex-start;
}

.radial-mindmap .branch {
    background: rgba(255, 255, 255, 0.1);
    padding: 15px;
    border-radius: 8px;
    margin: 0 10px;
    text-align: center;
    position: relative;
}

.radial-mindmap .branch:before {
    content: '↓';
    position: absolute;
    top: -35px;
    left: 50%;
    transform: translateX(-50%);
    color: white;
    font-size: 24px;
}

.radial-mindmap a {
    color: lightblue;
    text-decoration: none;
}

.radial-mindmap a:hover {
    text-decoration: underline;
}

/* ================================
   RESPONSIVE DESIGN - MOBILE FIRST
   ================================ */

/* Mobile styles (up to 480px) */
@media screen and (max-width: 480px) {
    body {
        font-size: 14px;
        background-size: 100% 100%;
    }
    
    header {
        padding: 0.5em;
    }
    
    /* Hide KALYNK_AN TUỆ text on mobile */
    header div:first-child {
        display: none;
    }
    
    /* Make section title larger (1.5x) */
    #kham-pha h2 {
        font-size: 1.5em !important;
    }
    
    #kham-pha small {
        font-size: 1.2em !important;
    }
    
    .buttons {
        flex-direction: column;
        gap: 0.5em;
        padding: 0 10px;
    }
    
    .button {
        padding: 0.8em 1em;
        font-size: 0.95em;
        white-space: normal;
        line-height: 1.4;
    }
    
    section {
        padding: 1em;
        margin: 0.5em;
        width: auto !important;
        max-width: none !important;
    }
    
    .buttons {
        margin-top: 10px;
    }
    
    section h2 {
        font-size: 1em;
    }
    
    section p {
        font-size: 0.85em;
        line-height: 1.4;
    }
    
    img {
        max-width: 100%;
        margin: 0.5em 0;
    }
    
    .gallery {
        flex-direction: column;
        align-items: center;
    }
    
    .gallery img {
        width: 100%;
        max-width: 100%;
    }
    
    .albums {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .flow-mindmap {
        flex-direction: column;
        margin: 20px 0;
    }
    
    .flow-mindmap .center {
        margin-right: 0;
        margin-bottom: 15px;
        width: 100%;
        text-align: center;
    }
    
    .flow-mindmap .branches {
        width: 100%;
    }
    
    .flow-mindmap .branch {
        flex-direction: column;
        align-items: flex-start;
    }
    
    .flow-mindmap .arrow {
        display: none;
    }
    
    .flow-mindmap .node {
        width: 100%;
        box-sizing: border-box;
    }
    
    .flow-mindmap .sub-branches {
        margin-left: 10px;
    }
    
    .mindmap {
        flex-direction: column;
    }
    
    .mindmap .root {
        margin-right: 0;
        margin-bottom: 15px;
        width: 100%;
        text-align: center;
    }
    
    .mindmap .root:after {
        display: none;
    }
    
    .mindmap .branch {
        width: 100%;
        margin-bottom: 10px;
    }
    
    .mindmap .node:before {
        display: none;
    }
    
    .radial-mindmap .branches {
        flex-direction: column;
        align-items: center;
    }
    
    .radial-mindmap .branch {
        margin: 10px 0;
        width: 80%;
    }
    
    video {
        width: 100%;
        max-width: 100%;
    }
    
    #video-reviews {
        padding: 20px 10px;
    }
    
    #video-reviews div[style*="display: flex"] {
        flex-direction: column !important;
        gap: 20px !important;
    }
    
    #video-reviews div[style*="flex: 1"] {
        max-width: 100% !important;
        min-width: 100% !important;
    }
    
    #video-reviews blockquote {
        max-width: 100% !important;
        min-width: 100% !important;
    }
    
    #video-reviews p {
        font-size: 0.85em;
        padding: 0 10px;
    }
    
    .dropdown-content {
        min-width: 120px;
    }
    
    .dropdown-content a {
        padding: 8px 10px;
        font-size: 11px;
    }
    
    /* Founder section mobile styles */
    #founder {
        flex-direction: column !important;
        gap: 15px !important;
    }
    
    #founder div {
        min-width: 100% !important;
        padding-left: 0 !important;
        padding: 15px !important;
    }
    
    #founder blockquote {
        max-width: 100% !important;
        min-width: 100% !important;
    }
}

/* Tablet styles (481px to 768px) */
@media screen and (min-width: 481px) and (max-width: 768px) {
    body {
        font-size: 15px;
    }
    
    header div:first-child {
        font-size: 2em !important;
    }
    
    .buttons {
        flex-wrap: wrap;
        gap: 0.4em;
    }
    
    .button {
        flex: 1 1 45%;
        font-size: 0.95em;
    }
    
    section {
        padding: 1.5em;
        margin: 0.8em;
    }
    
    img {
        max-width: 200px;
    }
    
    .gallery {
        flex-wrap: wrap;
    }
    
    .albums {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .flow-mindmap {
        flex-wrap: wrap;
    }
    
    .flow-mindmap .branches {
        width: 100%;
    }
    
    #video-reviews div[style*="display: flex"] {
        gap: 20px !important;
    }
    
    #video-reviews div[style*="flex: 1"] {
        min-width: 45% !important;
    }
}

/* Desktop styles (769px and above) */
@media screen and (min-width: 769px) {
    .buttons {
        flex-wrap: nowrap;
    }
    
    .button {
        flex: 1;
        white-space: nowrap;
    }
    
    section {
        max-width: 800px;
    }
    
    .gallery {
        flex-wrap: wrap;
    }
    
    .albums {
        grid-template-columns: repeat(4, 1fr);
    }
}

/* Large desktop styles (1200px and above) */
@media screen and (min-width: 1200px) {
    body {
        font-size: 18px;
    }
    
    section {
        max-width: 1000px;
    }
    
    img {
        max-width: 300px;
    }
}