body {
    margin: 0;
    font-family: 'Segoe UI', -apple-system, Arial, sans-serif;
    background: linear-gradient(-45deg, #1a365d, #2a4365, #2b6cb0, #3182ce);
    background-size: 400% 400%;
    animation: gradientBG 15s ease infinite;
    color: white;
    min-height: 100vh;
    padding: 30px 20px;
    box-sizing: border-box;
}

.back-btn {
    display: inline-block;
    color: white;
    text-decoration: none;
    margin-bottom: 20px;
    font-weight: 500;
    background: rgba(255, 255, 255, 0.15);
    padding: 6px 16px;
    border-radius: 4px;
    border: 1px solid rgba(255, 255, 255, 0.3);
    border-top-color: rgba(255, 255, 255, 0.5);
    border-left-color: rgba(255, 255, 255, 0.5);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    box-shadow: 0 4px 10px rgba(0,0,0,0.2), inset 0 1px 0 rgba(255,255,255,0.2);
    transition: all 0.2s;
}
.back-btn:hover { 
    background: rgba(255, 255, 255, 0.25); 
    box-shadow: 0 4px 15px rgba(255,255,255,0.2);
}

h1 {
    text-align: center;
    margin: 0 0 10px 0;
    font-weight: 400;
    letter-spacing: 0.5px;
    text-shadow: 0 2px 8px rgba(0, 0, 0, 0.6);
}

.subtitle {
    text-align: center;
    color: #d1d5db;
    margin-bottom: 35px;
    text-shadow: 0 1px 4px rgba(0, 0, 0, 0.4);
}

/* VISTA HUB GRID SELECTION ARCHITECTURE */
.hub-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 20px;
    max-width: 1200px;
    margin: 0 auto 40px auto;
}

.hub-card {
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.03) 100%);
    backdrop-filter: blur(15px);
    -webkit-backdrop-filter: blur(15px);
    border: 1px solid rgba(255, 255, 255, 0.25);
    border-top-color: rgba(255, 255, 255, 0.45);
    border-left-color: rgba(255, 255, 255, 0.45);
    border-radius: 8px;
    padding: 25px 20px;
    text-align: center;
    cursor: pointer;
    box-shadow: 0 10px 25px rgba(0,0,0,0.25), inset 0 1px 0 rgba(255,255,255,0.1);
    transition: all 0.3s cubic-bezier(0.165, 0.84, 0.44, 1);
}

.hub-card:hover {
    transform: translateY(-4px);
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.18) 0%, rgba(255, 255, 255, 0.06) 100%);
    border-color: rgba(255, 255, 255, 0.4);
    box-shadow: 0 15px 35px rgba(0,0,0,0.35);
}

.hub-card.active-hub {
    background: linear-gradient(135deg, rgba(43, 108, 176, 0.4) 0%, rgba(26, 54, 93, 0.4) 100%);
    border-color: #63b3ed;
    box-shadow: 0 0 15px rgba(99, 179, 237, 0.4);
}

.hub-icon { font-size: 2.5rem; margin-bottom: 12px; display: block; }
.hub-title { font-size: 1.15rem; font-weight: 500; margin: 0; line-height: 1.4; }

/* MATHEMATICS DRILLDOWN SECTION */
.math-flow-section {
    max-width: 1200px;
    margin: 0 auto 30px auto;
    animation: fadeInSlide 0.4s ease forwards;
}

.drilldown-header {
    display: flex;
    align-items: center;
    gap: 14px;
    margin-bottom: 20px;
}

.back-drill-btn {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    color: white;
    font-weight: 600;
    font-size: 0.85rem;
    font-family: inherit;
    background: rgba(255, 255, 255, 0.15);
    padding: 6px 14px;
    border-radius: 4px;
    border: 1px solid rgba(255, 255, 255, 0.3);
    cursor: pointer;
    backdrop-filter: blur(6px);
    -webkit-backdrop-filter: blur(6px);
    transition: all 0.2s ease;
}

.back-drill-btn:hover {
    background: rgba(255, 255, 255, 0.28);
    box-shadow: 0 0 12px rgba(99, 179, 237, 0.35);
}

.drilldown-breadcrumb {
    font-size: 0.95rem;
    color: #93c5fd;
    font-weight: 500;
    text-shadow: 0 1px 3px rgba(0, 0, 0, 0.5);
}

.math-subgrid {
    margin-bottom: 20px;
    animation: fadeInSlide 0.35s ease forwards;
}

.hub-card-desc {
    display: block;
    margin-top: 6px;
    font-size: 0.8rem;
    color: #cbd5e1;
}

.card-disabled {
    opacity: 0.55;
    cursor: not-allowed;
    filter: grayscale(40%);
}

.card-disabled:hover {
    transform: none;
    box-shadow: 0 10px 25px rgba(0,0,0,0.25);
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.03) 100%);
    border-color: rgba(255, 255, 255, 0.25);
}

.badge-coming-soon {
    display: inline-block;
    margin-top: 8px;
    padding: 2px 8px;
    border-radius: 3px;
    background: rgba(239, 68, 68, 0.25);
    border: 1px solid rgba(239, 68, 68, 0.4);
    color: #fca5a5;
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* YOUTUBE STUDIO TABLE DISPLAY WRAPPER */
.table-display-section {
    display: none;
    max-width: 1200px;
    margin: 0 auto;
    animation: fadeInSlide 0.5s ease forwards;
}

.table-container {
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.08) 0%, rgba(255, 255, 255, 0.03) 100%);
    backdrop-filter: blur(25px) saturate(180%);
    -webkit-backdrop-filter: blur(25px) saturate(180%);
    border: 1px solid rgba(255, 255, 255, 0.35);
    border-top-color: rgba(255, 255, 255, 0.55);
    border-left-color: rgba(255, 255, 255, 0.55);
    border-radius: 8px;
    box-shadow: 0 25px 60px rgba(0, 0, 0, 0.45), inset 0 1px 0 rgba(255, 255, 255, 0.2);
    overflow-x: auto;
}

.studio-table { width: 100%; border-collapse: collapse; text-align: left; min-width: 850px; }

.studio-table th {
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.12) 0%, rgba(255, 255, 255, 0.02) 100%);
    padding: 16px 20px; font-weight: 500; font-size: 0.9rem; color: #bfdbfe;
    border-bottom: 2px solid rgba(255, 255, 255, 0.25); text-shadow: 0 1px 3px rgba(0,0,0,0.6);
}

.studio-table td {
    padding: 18px 20px; border-bottom: 1px solid rgba(255, 255, 255, 0.15);
    font-size: 0.95rem; vertical-align: middle; text-shadow: 0 1px 2px rgba(0, 0, 0, 0.4);
}

.studio-table tr:hover { background: linear-gradient(90deg, rgba(255, 255, 255, 0.06) 0%, rgba(255, 255, 255, 0.01) 100%); }
.title-block { display: flex; flex-direction: column; gap: 6px; }
.video-title-txt { font-weight: 500; color: #ffffff; line-height: 1.4; }
.meta-tags { display: flex; flex-wrap: wrap; gap: 6px; }

.attribute-badge {
    font-size: 0.7rem; font-weight: 600; background: rgba(0, 0, 0, 0.25);
    border: 1px solid rgba(255, 255, 255, 0.15); padding: 2px 6px; border-radius: 3px; color: #93c5fd; text-transform: uppercase;
}

/* BUTTON CONTROL LAYER ELEMENTS */
.btn-studio {
    display: inline-flex; align-items: center; justify-content: center; gap: 6px; padding: 8px 16px; border-radius: 4px; font-size: 0.85rem; font-weight: 500; cursor: pointer; text-decoration: none; transition: all 0.2s ease; white-space: nowrap; border: 1px solid rgba(255, 255, 255, 0.25); border-top-color: rgba(255, 255, 255, 0.4); border-left-color: rgba(255, 255, 255, 0.4); box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2), inset 0 1px 0 rgba(255, 255, 255, 0.1);
}
.btn-play { background: linear-gradient(180deg, rgba(239, 68, 68, 0.25) 0%, rgba(185, 28, 28, 0.15) 100%); color: #fca5a5; border-color: rgba(239, 68, 68, 0.4); }
.btn-play:hover { background: linear-gradient(180deg, rgba(239, 68, 68, 0.4) 0%, rgba(185, 28, 28, 0.25) 100%); border-color: rgba(239, 68, 68, 0.6); color: #ffffff; box-shadow: 0 0 10px rgba(239, 68, 68, 0.4); }
.btn-download { background: linear-gradient(180deg, rgba(255, 255, 255, 0.12) 0%, rgba(255, 255, 255, 0.02) 100%); color: #e2e8f0; }
.btn-download:hover { background: linear-gradient(180deg, rgba(255, 255, 255, 0.22) 0%, rgba(255, 255, 255, 0.07) 100%); border-color: rgba(255, 255, 255, 0.4); color: white; }
.btn-quiz { background: linear-gradient(180deg, rgba(59, 130, 246, 0.25) 0%, rgba(29, 78, 216, 0.15) 100%); color: #93c5fd; border-color: rgba(59, 130, 246, 0.4); }
.btn-quiz:hover { background: linear-gradient(180deg, rgba(59, 130, 246, 0.4) 0%, rgba(29, 78, 216, 0.25) 100%); border-color: rgba(59, 130, 246, 0.6); color: white; box-shadow: 0 0 10px rgba(59, 130, 246, 0.4); }

.row-lang-selector { display: flex; gap: 5px; }
.lang-pill { padding: 2px 6px; font-size: 0.7rem; border-radius: 3px; background: rgba(0,0,0,0.3); border: 1px solid rgba(255,255,255,0.1); color: #cbd5e1; cursor: pointer; font-weight: 600; }
.lang-pill.active { background: linear-gradient(180deg, #3182ce 0%, #2b6cb0 100%); border-color: rgba(255,255,255,0.3); color: white; }

/* STUDY / PRACTICE MINI BUTTONS */
.pdf-mini-actions {
    display: flex;
    justify-content: center;
    gap: 5px;
    margin-top: 7px;
}

.pdf-mini-btn {
    padding: 2px 8px;
    font-size: 0.7rem;
    border-radius: 3px;
    background: rgba(0, 0, 0, 0.3);
    border: 1px solid rgba(255, 255, 255, 0.15);
    color: #cbd5e1;
    cursor: pointer;
    font-weight: 600;
    font-family: inherit;
    transition: all 0.2s ease;
}

.pdf-mini-btn:hover {
    background: linear-gradient(180deg, #3182ce 0%, #2b6cb0 100%);
    border-color: rgba(255, 255, 255, 0.3);
    color: white;
}

@keyframes gradientBG {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}
@keyframes fadeInSlide {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}