body, html {
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', 'Microsoft JhengHei', Arial, sans-serif;
    min-height: 100vh;
    position: relative;
    background: #222;
}
.background {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: url('images/vtc.jpg') no-repeat center center/cover;
    filter: brightness(0.5) blur(2px);
    z-index: 0;
}
header {
    background: rgba(34, 34, 34, 0.85);
    color: #fff;
    padding: 0.5rem 0;
    position: relative;
    z-index: 2;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}
.container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 2rem;
}
nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    gap: 1.5rem;
}
nav a {
    color: #fff;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.2s;
}
nav a:hover {
    color: #ffb300;
}
.hero.hero-large {
    min-height: 55vh;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    background: url('images/vtc.jpg') no-repeat center center;
    background-size: cover;
    box-shadow: 0 2px 16px rgba(0,0,0,0.08);
    border-radius: 0 0 16px 16px;
    z-index: 2;
}
.hero-large::before {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(20, 28, 38, 0.38);
    z-index: 1;
    border-radius: 0 0 16px 16px;
}
.hero-content {
    position: relative;
    z-index: 2;
    text-align: center;
    width: 100%;
}
.hero-content h2 {
    color: #fff;
    font-size: 3rem;
    font-weight: 800;
    letter-spacing: 2px;
    margin-bottom: 1.2rem;
    text-shadow: 0 4px 24px rgba(0,0,0,0.18);
}
.hero-subtitle {
    color: #fff;
    font-size: 1.25rem;
    font-weight: 400;
    margin-bottom: 2.2rem;
    text-shadow: 0 2px 8px rgba(0,0,0,0.13);
}
.hero-content .join-btn {
    margin-top: 0;
    font-size: 1.1rem;
    padding: 0.8rem 2.1rem;
    border: 2px solid #fff;
    background: transparent;
    color: #fff;
    box-shadow: 0 2px 12px rgba(63,81,181,0.13);
    transition: background 0.2s, color 0.2s, border 0.2s, box-shadow 0.2s, transform 0.15s;
    text-decoration: none;
    border-bottom: none;
}
.hero-content .join-btn:hover {
    background: #fff;
    color: #3f51b5;
    border: 2px solid #3f51b5;
    box-shadow: 0 6px 24px rgba(33,150,243,0.18);
    transform: translateY(-2px) scale(1.04);
}
footer {
    background: rgba(34, 34, 34, 0.9);
    color: #fff;
    padding: 1.5rem 0 1rem 0;
    text-align: center;
    position: relative;
    z-index: 2;
    margin-top: 5vh;
    box-shadow: 0 -2px 8px rgba(0,0,0,0.1);
}
.footer-container {
    max-width: 900px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
}
.footer-links a {
    color: #ffb300;
    text-decoration: none;
    margin: 0 0.5rem;
    font-size: 1rem;
}
.footer-links a:hover {
    text-decoration: underline;
}
@media (max-width: 768px) {
    .container {
        flex-direction: column;
        padding: 0 1rem;
        gap: 0.5rem;
    }
    nav ul {
        flex-direction: column;
        gap: 0.8rem;
    }
    .hero.hero-large {
        min-height: 38vh;
    }
    .hero-content h2 {
        font-size: 2rem;
    }
    .hero-subtitle {
        font-size: 1rem;
    }
    .footer-container {
        padding: 0 1rem;
    }
}
.intro-section {
    background: rgba(245, 247, 249, 0.95);
    margin: 3rem 0 0 0;
    padding: 2.5rem 0 1.5rem 0;
    text-align: center;
    border-radius: 12px;
    box-shadow: 0 2px 16px rgba(0,0,0,0.04);
    position: relative;
    z-index: 2;
}
.section-title {
    font-size: 2rem;
    font-weight: 700;
    color: #333;
    margin-bottom: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1.2rem;
}
.section-title span {
    display: inline-block;
    width: 60px;
    height: 2px;
    background: #3f51b5;
    border-radius: 2px;
}
.intro-text {
    color: #444;
    font-size: 1.15rem;
    max-width: 700px;
    margin: 0 auto;
    line-height: 1.8;
}
.features-section {
    background: rgba(245, 247, 249, 0.95);
    padding: 2.5rem 0 3rem 0;
    margin-bottom: 2rem;
    border-radius: 0 0 12px 12px;
    box-shadow: 0 2px 16px rgba(0,0,0,0.04);
    position: relative;
    z-index: 2;
}
.features-grid {
    display: flex;
    flex-direction: row;
    justify-content: center;
    align-items: stretch;
    gap: 2.5rem;
    max-width: 1200px;
    margin: 0 auto;
    flex-wrap: nowrap;
}
.feature-card {
    background: #fff;
    border-radius: 10px;
    box-shadow: 0 2px 12px rgba(0,0,0,0.07);
    padding: 2.2rem 2rem 1.5rem 2rem;
    width: 320px;
    min-height: 240px;
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    transition: box-shadow 0.2s;
    position: relative;
}
.feature-card:hover {
    box-shadow: 0 6px 24px rgba(63,81,181,0.13);
}
.feature-icon {
    font-size: 2.5rem;
    margin-bottom: 1.2rem;
    color: #3f51b5;
    align-self: flex-start;
}
.feature-card h3 {
    color: #2d3a4b;
    font-size: 1.25rem;
    font-weight: 700;
    margin: 0 0 0.5rem 0;
    position: relative;
    cursor: pointer;
}
.feature-underline {
    width: 60px;
    height: 3px;
    background: #3f51b5;
    border-radius: 2px;
    margin-bottom: 1rem;
    transition: width 0.35s cubic-bezier(.4,1.6,.6,1), background 0.25s;
}
.feature-card h3:hover + .feature-underline,
.feature-card h3:focus + .feature-underline {
    width: 100px;
    background: #2196f3;
}
.feature-card p {
    color: #444;
    font-size: 1rem;
    margin: 0;
}
@media (max-width: 1100px) {
    .features-grid {
        gap: 1.2rem;
        flex-wrap: wrap;
    }
    .feature-card {
        width: 90vw;
        max-width: 400px;
    }
}
@media (max-width: 900px) {
    .features-grid {
        flex-direction: column;
        align-items: center;
        flex-wrap: nowrap;
    }
    .feature-card {
        width: 95vw;
        max-width: 420px;
    }
}
.intro-flex {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 2.5rem;
    max-width: 900px;
    margin: 0 auto;
}
.intro-logo {
    width: 120px;
    height: 120px;
    object-fit: contain;
    border-radius: 16px;
    box-shadow: 0 2px 12px rgba(63,81,181,0.08);
    background: #fff;
}
.intro-content {
    flex: 1;
    min-width: 0;
}
@media (max-width: 700px) {
    .intro-flex {
        flex-direction: column;
        gap: 1.2rem;
    }
    .intro-logo {
        width: 90px;
        height: 90px;
    }
}
.lang-dropdown {
    position: relative;
    overflow: visible;
    z-index: 1001;
}
#langBtn {
    background: transparent;
    color: #fff;
    border: none;
    font-size: 1rem;
    font-family: inherit;
    cursor: pointer;
    padding: 0.3rem 1rem;
    border-radius: 6px;
    transition: background 0.2s;
}
#langBtn:hover, #langBtn:focus {
    background: #3f51b5;
    color: #fff;
}
.lang-menu {
    display: none;
    position: absolute;
    right: 0;
    top: 2.2rem;
    background: #fff;
    color: #333;
    min-width: 120px;
    box-shadow: 0 4px 16px rgba(0,0,0,0.13);
    border-radius: 8px;
    z-index: 2000;
    padding: 0.3rem 0;
    list-style: none;
    overflow: visible;
}
.lang-dropdown.open .lang-menu {
    display: block;
}
.lang-menu li {
    padding: 0.7rem 1.2rem;
    cursor: pointer;
    transition: background 0.18s, color 0.18s;
    border-radius: 4px;
}
.lang-menu li:hover {
    background: #3f51b5;
    color: #fff;
}
.lang-switch-group {
    display: flex;
    gap: 0.3rem;
    align-items: center;
    margin-left: 1rem;
}
.lang-switch {
    background: transparent;
    color: #fff;
    border: 1.5px solid #fff;
    font-size: 1rem;
    font-family: inherit;
    cursor: pointer;
    padding: 0.25rem 0.9rem;
    border-radius: 6px;
    transition: background 0.2s, color 0.2s, border 0.2s;
    outline: none;
    width: 60px;
    min-width: 60px;
    max-width: 60px;
    text-align: center;
    box-sizing: border-box;
}
.lang-switch.active, .lang-switch:focus {
    background: #3f51b5;
    color: #fff;
    border: 1.5px solid #3f51b5;
}
.lang-switch:hover {
    background: #2196f3;
    color: #fff;
    border: 1.5px solid #2196f3;
}