/* Grammar Practice - UltraCirculum Hub Theme */
:root {
    /* Category Colors - UltraCirculum Theme */
    --tenses-color: #2196F3;
    --modals-color: #FFB74D;
    --nouns-color: #BA68C8;
    --vocabulary-color: #F06292;
    --communication-color: #00BCD4;
    --conditionals-color: #8BC34A;
    --advanced-color: #F8877F;
    
    /* UltraCirculum Admin Theme */
    --admin-bg: #030712;
    --admin-card: rgba(17, 24, 39, 0.7);
    --admin-border: rgba(59, 130, 246, 0.15);
    --admin-border-glow: 0 0 1px rgba(59, 130, 246, 0.15);
    --admin-shadow: 0 8px 25px -5px rgba(0, 0, 0, 0.4), 0 4px 10px -2px rgba(0, 0, 0, 0.3);
    --shadow-hover: 0 12px 30px -8px rgba(0, 0, 0, 0.5), 0 6px 15px -3px rgba(0, 0, 0, 0.4);
    
    /* Colors */
    --white: #ffffff;
    --text-light: rgba(255, 255, 255, 0.7);
    --border-radius: 16px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ═══ STARS & FIREFLIES CANVAS ═══ */
.stars, .fireflies, .fireflies-front {
    position: fixed;
    left: 0;
    top: 0;
    width: 100vw;
    height: 100vh;
    pointer-events: none;
    -webkit-user-select: none;
    user-select: none;
}

.stars { z-index: 0; }
.fireflies { z-index: 1; }
.fireflies-front { z-index: 2; }

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--admin-bg);
    min-height: 100vh;
    line-height: 1.6;
    color: var(--white);
    overflow-x: hidden;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0;
    position: relative;
    z-index: 10;
}

/* Header Section - 20% transparency and 3px blur */
.header {
    text-align: center;
    margin: 0 auto 20px auto;
    max-width: 1400px;
    padding: 32px 20px;
    background: rgba(15, 15, 40, 0.3);
    border-radius: var(--border-radius);
    border: 1px solid rgba(255, 255, 255, 0.08);
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.7);
    position: relative;
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

/* Top Navigation Header */
.top-navigation-header {
    display: flex;
    justify-content: flex-start;
    align-items: center;
    padding: 15px 20px;
    margin: 0 auto 20px auto;
    max-width: 1400px;
    background: rgba(15, 15, 40, 0.3);
    border-radius: var(--border-radius);
    border: 1px solid rgba(255, 255, 255, 0.08);
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
    position: relative;
    z-index: 20;
    box-sizing: border-box;
}

/* Home Button - 20% transparency and 3px blur */
.home-btn {
    background: rgba(15, 15, 40, 0.3);
    border: 1px solid rgba(255, 255, 255, 0.08);
    cursor: pointer;
    padding: 6px;
    border-radius: 8px;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
    margin-left: 20px;
}

.home-btn:hover {
    background: rgba(59, 130, 246, 0.2);
    box-shadow: 0 2px 8px rgba(59, 130, 246, 0.3);
}

.home-icon {
    width: 20px;
    height: 20px;
    color: rgba(255, 255, 255, 0.8);
    transition: var(--transition);
}

.home-btn:hover .home-icon {
    color: #3B82F6;
}

/* Title Logo */
.title-logo {
    max-width: 340px;
    width: 100%;
    height: auto;
    margin-bottom: 8px;
    filter: drop-shadow(0 4px 8px rgba(0, 0, 0, 0.3));
}

.copyright {
    font-size: 0.8125rem;
    margin-top: 0;
    margin-bottom: 8px;
    text-align: center;
    font-weight: 500;
    color: var(--text-light);
    opacity: 0.9;
}

.header h1 {
    font-size: 3.5em;
    font-weight: 700;
    background: linear-gradient(135deg, var(--white), #60a5fa);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    margin-bottom: 15px;
}

.header p {
    font-size: 1.3em;
    color: var(--text-light);
    font-weight: 300;
}

/* Search Section - 20% transparency and 3px blur */
.search-section {
    background: rgba(15, 15, 40, 0.3);
    padding: 30px 20px;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.7);
    margin: 0 auto 20px auto;
    max-width: 1400px;
    border: 1px solid rgba(255, 255, 255, 0.08);
    /* Cross-browser backdrop-filter support */
    -webkit-backdrop-filter: blur(3px);
    backdrop-filter: blur(3px);
    box-sizing: border-box;
}

#searchInput {
    width: 100%;
    padding: 15px 20px;
    font-size: 1.1em;
    border: 1px solid rgba(255, 255, 255, 0.08);
    border-radius: var(--border-radius);
    outline: none;
    transition: var(--transition);
    margin-bottom: 20px;
    background: rgba(15, 15, 40, 0.3);
    color: var(--white);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
}

#searchInput:focus {
    border-color: var(--tenses-color);
    box-shadow: 0 0 10px rgba(33, 150, 243, 0.3);
}

.filter-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: center;
}

.filter-btn {
    padding: 12px 24px;
    border: none;
    border-radius: 25px;
    background: rgba(15, 15, 40, 0.3);
    color: var(--white);
    cursor: pointer;
    font-size: 0.95em;
    font-weight: 500;
    transition: var(--transition);
    white-space: nowrap;
    border: 1px solid rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
}

.filter-btn:hover {
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
}

.filter-btn.active {
    background: var(--tenses-color);
    color: var(--white);
}

/* Perfect Grid Layout */
.masonry-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 25px;
    align-items: start;
    justify-content: center;
    margin: 0 auto;
    max-width: 1400px;
    padding: 0;
    box-sizing: border-box;
}

/* Grammar Cards - 20% transparency and 3px blur */
.grammar-card {
    background: rgba(15, 15, 40, 0.3);
    border-radius: var(--border-radius);
    padding: 20px;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.7);
    transition: var(--transition);
    cursor: pointer;
    position: relative;
    overflow: hidden;
    width: 100%;
    height: 320px;
    display: flex;
    flex-direction: column;
    border: 1px solid rgba(255, 255, 255, 0.08);
    /* Cross-browser backdrop-filter support */
    -webkit-backdrop-filter: blur(3px);
    backdrop-filter: blur(3px);
    /* Touch optimization */
    -webkit-tap-highlight-color: transparent;
    touch-action: manipulation;
}

.grammar-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: var(--tenses-color);
    transition: var(--transition);
}

.grammar-card:hover {
    box-shadow: var(--shadow-hover);
}

.grammar-card:hover::before {
    height: 100%;
    background: linear-gradient(135deg, var(--tenses-color), rgba(33, 150, 243, 0.8));
}

.grammar-card:hover .card-content {
    color: var(--white);
}

/* Category-specific hover effects */
.grammar-card.tenses::before { background: var(--tenses-color); }
.grammar-card.modals::before { background: var(--modals-color); }
.grammar-card.nouns::before { background: var(--nouns-color); }
.grammar-card.vocabulary::before { background: var(--vocabulary-color); }
.grammar-card.communication::before { background: var(--communication-color); }
.grammar-card.conditionals::before { background: var(--conditionals-color); }
.grammar-card.advanced::before { background: var(--advanced-color); }

.grammar-card.tenses:hover::before { 
    background: linear-gradient(135deg, var(--tenses-color), rgba(33, 150, 243, 0.8)); 
}
.grammar-card.modals:hover::before { 
    background: linear-gradient(135deg, var(--modals-color), rgba(255, 183, 77, 0.8)); 
}
.grammar-card.nouns:hover::before { 
    background: linear-gradient(135deg, var(--nouns-color), rgba(186, 104, 200, 0.8)); 
}
.grammar-card.vocabulary:hover::before { 
    background: linear-gradient(135deg, var(--vocabulary-color), rgba(240, 98, 146, 0.8)); 
}
.grammar-card.communication:hover::before { 
    background: linear-gradient(135deg, var(--communication-color), rgba(0, 188, 212, 0.8)); 
}
.grammar-card.conditionals:hover::before { 
    background: linear-gradient(135deg, var(--conditionals-color), rgba(139, 195, 74, 0.8)); 
}
.grammar-card.advanced:hover::before { 
    background: linear-gradient(135deg, var(--advanced-color), rgba(248, 135, 127, 0.8)); 
}

.card-content {
    position: relative;
    z-index: 2;
    transition: var(--transition);
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
}

.card-title {
    font-size: 1.4em;
    font-weight: 600;
    margin-bottom: 12px;
    color: var(--white);
    text-transform: capitalize;
}

.card-category {
    display: inline-block;
    padding: 4px 12px;
    background: rgba(15, 15, 40, 0.3);
    color: var(--text-light);
    border-radius: 15px;
    font-size: 0.85em;
    margin-bottom: 15px;
    font-weight: 500;
    border: 1px solid rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
}

.card-description {
    color: var(--text-light);
    margin-bottom: 20px;
    font-size: 0.95em;
}

.card-stats {
    display: flex;
    justify-content: space-between;
    margin-bottom: 20px;
    font-size: 0.9em;
}

.stat-item {
    text-align: center;
}

.stat-number {
    font-weight: 600;
    color: var(--white);
    display: block;
}

.stat-label {
    color: var(--text-light);
    font-size: 0.85em;
}

/* Loading Animation - 20% transparency and 3px blur */
.loading {
    text-align: center;
    padding: 50px;
    color: var(--white);
    font-size: 1.2em;
    background: rgba(15, 15, 40, 0.3);
    border-radius: var(--border-radius);
    border: 1px solid rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
}

.loading::after {
    content: '';
    display: inline-block;
    width: 30px;
    height: 30px;
    border: 3px solid var(--white);
    border-radius: 50%;
    border-top-color: transparent;
    animation: spin 1s linear infinite;
    margin-left: 15px;
    vertical-align: middle;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Responsive Design */
@media (max-width: 1200px) {
    .masonry-container {
        grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
        gap: 20px;
    }
}

@media (max-width: 900px) {
    .container {
        padding: 0;
    }
    
    .masonry-container {
        grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
        gap: 18px;
        padding: 0;
    }
    
    .grammar-card {
        height: auto; /* Allow dynamic height */
        min-height: 320px; /* Minimum height for consistency */
        padding: 18px;
    }
    
    .card-content {
        min-height: 250px; /* Ensure content has enough space */
    }
    
    .header h1 {
        font-size: 2.8em;
    }
    
    .filter-buttons {
        gap: 8px;
    }
    
    .filter-btn {
        padding: 10px 18px;
        font-size: 0.9em;
    }
}

/* Enhanced Mobile Design (≤768px) - FIXED CARD VISIBILITY */
@media (max-width: 768px) {
    .container {
        padding: 0;
    }
    
    .header {
        margin-bottom: 20px;
        padding: 20px 20px;
    }
    
    .top-navigation-header {
        padding: 10px 15px;
        margin-bottom: 20px;
    }
    
    .home-btn {
        padding: 5px;
        width: 32px;
        height: 32px;
        margin-left: 15px;
    }
    
    .home-icon {
        width: 18px;
        height: 18px;
    }
    
    .title-logo {
        max-width: 280px;
        margin-bottom: 10px;
    }
    
    .header h1 {
        font-size: 2.4em;
        margin-bottom: 10px;
    }
    
    .header p {
        font-size: 1.05em;
    }
    
    .search-section {
        padding: 18px;
        margin-bottom: 20px;
    }
    
    #searchInput {
        padding: 12px 16px;
        font-size: 1rem;
        margin-bottom: 15px;
    }
    
        /* Cross-browser scrollbar fixes - Enhanced compatibility */
        .filter-buttons {
            gap: 6px;
            justify-content: flex-start;
            overflow-x: auto;
            padding-bottom: 8px;
            /* IE and Edge */
            -ms-overflow-style: none;
        }
        
        /* Webkit browsers (Chrome, Safari, Edge) */
        .filter-buttons::-webkit-scrollbar {
            width: 0;
            height: 0;
            display: none;
        }
        
        /* Firefox (supports scrollbar-width but needs fallbacks for older versions) */
        @supports (scrollbar-width: none) {
            .filter-buttons {
                scrollbar-width: none;
            }
        }
    
        /* Cross-browser min-width support - Enhanced compatibility */
        .filter-btn {
            padding: 8px 16px;
            font-size: 0.85em;
            flex-shrink: 0;
            /* Samsung Internet 5.0+ support */
            min-width: -webkit-fill-available;
            /* Firefox support */
            min-width: -moz-available;
        }
        
        /* Modern browsers with fit-content support */
        @supports (min-width: fit-content) {
            .filter-btn {
                min-width: fit-content;
            }
        }
    
    .masonry-container {
        grid-template-columns: 1fr;
        gap: 16px;
        padding: 0 10px;
    }
    
    .grammar-card {
        height: auto; /* Allow dynamic height */
        min-height: 310px; /* Minimum height for consistency */
        padding: 16px;
        margin: 0 auto;
        max-width: 100%;
        min-width: 280px;
    }
    
    .card-content {
        min-height: 240px; /* Ensure content has enough space */
    }
    
    .card-title {
        font-size: 1.25em;
        margin-bottom: 10px;
    }
    
    .card-description {
        font-size: 0.9em;
        margin-bottom: 15px;
        line-height: 1.5;
    }
    
    .card-stats {
        font-size: 0.85em;
        margin-bottom: 15px;
    }
}

/* Ultra Mobile - Small Phones (≤480px) - FIXED CARD VISIBILITY */
@media (max-width: 480px) {
    .container {
        padding: 0;
    }
    
    .header {
        padding: 16px 15px;
        margin-bottom: 20px;
    }
    
    .home-btn {
        padding: 4px;
        width: 28px;
        height: 28px;
        margin-left: 12px;
    }
    
    .home-icon {
        width: 16px;
        height: 16px;
    }
    
    .title-logo {
        max-width: 240px;
        margin-bottom: 8px;
    }
    
    .header h1 {
        font-size: 2em;
        line-height: 1.2;
    }
    
    .header p {
        font-size: 1rem;
    }
    
    .search-section {
        padding: 15px;
        margin-bottom: 20px;
    }
    
    .masonry-container {
        gap: 12px;
        padding: 0 10px;
    }
    
    .grammar-card {
        height: auto; /* Allow dynamic height */
        min-height: 340px; /* Increased minimum height for small screens */
        padding: 15px;
        min-width: 260px;
        max-width: calc(100vw - 26px);
    }
    
    .card-content {
        min-height: 260px; /* Ensure content has enough space */
    }
    
    .card-title {
        font-size: 1.15em;
        margin-bottom: 8px;
    }
    
    .card-description {
        font-size: 0.85em;
        line-height: 1.4;
        margin-bottom: 15px;
    }
    
    .card-stats {
        flex-direction: column;
        gap: 8px;
        margin-bottom: 15px;
    }
    
    .stat-item {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 6px 10px;
        background: rgba(15, 15, 40, 0.3);
        border-radius: 8px;
        backdrop-filter: blur(3px);
        -webkit-backdrop-filter: blur(3px);
        border: 1px solid rgba(255, 255, 255, 0.08);
    }
    
    .stat-number {
        display: inline;
        margin-right: 5px;
    }
}

/* Touch-friendly hover alternatives for mobile */
@media (max-width: 768px) {
    .grammar-card:hover {
        /* No transform on mobile */
    }
    
    .grammar-card:active {
        opacity: 0.9;
        transition: opacity 0.1s ease;
    }
    
    .filter-btn:hover {
        /* No transform on mobile */
    }
    
    .filter-btn:active {
        opacity: 0.9;
        transition: opacity 0.1s ease;
    }
}