:root {
    /* New modern theme variables - Primary colors */
    --bg-primary: #f5f7fa;
    --bg-secondary: #ffffff;
    --text-primary: #2d3748;
    --text-secondary: #718096;
    --accent-color: #3b82f6;
    --accent-hover: #2563eb;
    --border-color: #e2e8f0;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.05), 0 1px 3px rgba(0, 0, 0, 0.1);
    --card-shadow-hover: 0 10px 15px rgba(0, 0, 0, 0.1), 0 4px 6px rgba(0, 0, 0, 0.05);
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --error-color: #ef4444;
}

[data-theme="dark"] {
    /* Dark theme variables */
    --bg-primary: #1a202c;
    --bg-secondary: #2d3748;
    --text-primary: #f7fafc;
    --text-secondary: #cbd5e0;
    --accent-color: #4299e1;
    --accent-hover: #63b3ed;
    --border-color: #4a5568;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.3), 0 1px 3px rgba(0, 0, 0, 0.2);
    --card-shadow-hover: 0 10px 15px rgba(0, 0, 0, 0.3), 0 4px 6px rgba(0, 0, 0, 0.2);
    --success-color: #059669;
    --warning-color: #d97706;
    --error-color: #dc2626;
}

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

body {
    font-family: 'Poppins', sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Header and Navigation */
header {
    background-color: var(--bg-secondary);
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

header.scrolled {
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.12);
}

nav {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo h1 {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--accent-color);
}

.logo h1 a {
    color: var(--accent-color);
    text-decoration: none;
    transition: color 0.2s, transform 0.2s;
    display: inline-block;
    background: linear-gradient(90deg, var(--accent-color), var(--accent-hover));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.logo h1 a:hover {
    transform: translateY(-1px);
}

.theme-toggle button {
    background: none;
    border: none;
    cursor: pointer;
    color: var(--text-secondary);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color 0.2s, transform 0.2s, box-shadow 0.2s;
    outline: none;
}

.theme-toggle button:hover {
    background-color: rgba(0, 0, 0, 0.05);
    transform: scale(1.1);
    box-shadow: 0 0 15px rgba(59, 130, 246, 0.4);
}

[data-theme="dark"] .theme-toggle button:hover {
    background-color: rgba(255, 255, 255, 0.1);
    box-shadow: 0 0 15px rgba(66, 153, 225, 0.4);
}

/* Main Content */
main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

.intro {
    text-align: center;
    margin-bottom: 3rem;
    animation: fadeInUp 0.8s ease-out;
}

.intro h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--accent-color);
    position: relative;
    display: inline-block;
}

.intro h2::after {
    content: '';
    position: absolute;
    width: 50%;
    height: 4px;
    background: linear-gradient(90deg, var(--accent-color), transparent);
    bottom: -10px;
    left: 25%;
    border-radius: 2px;
}

.intro p {
    font-size: 1.2rem;
    color: var(--text-secondary);
    max-width: 700px;
    margin: 0 auto;
}

/* Assignments Grid */
.assignments-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 2rem;
}

.assignment-card {
    background-color: var(--bg-secondary);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--card-shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease, opacity 0.3s ease;
    animation: fadeIn 0.6s ease-out forwards;
    opacity: 0;
}

.assignment-card:nth-child(1) { animation-delay: 0.1s; }
.assignment-card:nth-child(2) { animation-delay: 0.2s; }
.assignment-card:nth-child(3) { animation-delay: 0.3s; }
.assignment-card:nth-child(4) { animation-delay: 0.4s; }
.assignment-card:nth-child(5) { animation-delay: 0.5s; }

.assignment-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--card-shadow-hover);
}

.card-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    position: relative;
    overflow: hidden;
}

.card-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background-color: var(--accent-color);
    transition: transform 0.3s ease;
    transform: scaleY(0);
    transform-origin: bottom;
}

.assignment-card:hover .card-header::before {
    transform: scaleY(1);
}

.card-header h3 {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    transition: transform 0.3s ease;
}

.assignment-card:hover .card-header h3 {
    transform: translateX(8px);
}

.card-body {
    padding: 1.5rem;
}

.file-type {
    display: flex;
    align-items: center;
    margin-bottom: 1.5rem;
    color: var(--text-secondary);
}

.file-type svg {
    margin-right: 0.5rem;
    color: var(--accent-color);
}

.card-buttons {
    display: flex;
    justify-content: space-between;
    margin-top: 1.5rem;
}

.btn {
    display: inline-flex;
    align-items: center;
    padding: 0.5rem 1rem;
    border-radius: 6px;
    font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: all 0.2s ease;
    position: relative;
    overflow: hidden;
}

.btn svg {
    margin-right: 0.5rem;
    transition: transform 0.3s ease;
}

.btn-primary {
    background-color: var(--accent-color);
    color: white;
    border: none;
}

.btn-primary::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    transition: 0.5s;
}

.btn-primary:hover::before {
    left: 100%;
}

.btn-primary:hover {
    background-color: var(--accent-hover);
    transform: translateY(-3px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.25);
}

.btn-primary:hover svg {
    transform: translateX(3px);
}

.button-clicked {
    animation: buttonClick 0.3s ease;
}

@keyframes buttonClick {
    0% { transform: scale(1); }
    50% { transform: scale(0.95); }
    100% { transform: scale(1); }
}

.btn-outline {
    background-color: transparent;
    color: var(--accent-color);
    border: 1px solid var(--accent-color);
}

.btn-outline:hover {
    background-color: var(--accent-color);
    color: white;
    transform: translateY(-3px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.25);
}

.btn-outline:hover svg {
    transform: translateX(3px);
}

/* Assignment Details Page */
.assignment-navigation {
    display: flex;
    align-items: center;
    margin-bottom: 2rem;
    flex-wrap: wrap;
    gap: 1rem;
    animation: fadeIn 0.6s ease-out;
}

.back-btn {
    display: flex;
    align-items: center;
    color: var(--accent-color);
    text-decoration: none;
    font-weight: 500;
    transition: all 0.2s ease;
    margin-right: 1rem;
}

.back-btn:hover {
    color: var(--accent-hover);
    transform: translateX(-3px);
}

.back-btn svg {
    margin-right: 0.5rem;
    transition: transform 0.2s ease;
}

.back-btn:hover svg {
    transform: translateX(-2px);
}

/* Tabs */
.tabs-container {
    background-color: var(--bg-secondary);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--card-shadow);
    animation: fadeInUp 0.8s ease-out;
}

.tabs {
    display: flex;
    border-bottom: 1px solid var(--border-color);
    background: linear-gradient(to right, var(--bg-secondary), var(--bg-primary), var(--bg-secondary));
}

.tab-btn {
    padding: 1rem 1.5rem;
    background: none;
    border: none;
    cursor: pointer;
    font-weight: 500;
    color: var(--text-secondary);
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
    z-index: 1;
}

.tab-btn:hover {
    color: var(--accent-color);
}

.tab-btn::before {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 0;
    background-color: rgba(59, 130, 246, 0.08);
    transition: height 0.3s ease;
    z-index: -1;
}

.tab-btn:hover::before {
    height: 100%;
}

.tab-btn.active {
    color: var(--accent-color);
    font-weight: 600;
}

.tab-btn.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 3px;
    background: linear-gradient(90deg, transparent, var(--accent-color), transparent);
    border-radius: 3px 3px 0 0;
}

.tab-content {
    padding: 2rem;
}

.tab-pane {
    display: none;
}

.tab-pane.active {
    display: block;
    animation: fadeIn 0.4s ease;
}

.tab-changing {
    opacity: 0;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

@keyframes fadeInUp {
    from { 
        opacity: 0;
        transform: translateY(20px);
    }
    to { 
        opacity: 1;
        transform: translateY(0);
    }
}

/* PDF Container */
.docx-container {
    border: 1px solid var(--border-color);
    border-radius: 8px;
    overflow: hidden;
    transition: box-shadow 0.3s ease;
    min-height: 600px; /* Ensure container has height while loading */
}

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

.pdf-container {
    display: flex;
    flex-direction: column;
    height: 100%;
    background-color: var(--bg-secondary);
}

.pdf-container iframe, 
.pdf-container object {
    border: none;
    width: 100%;
    min-height: 600px;
    background-color: white;
    transition: opacity 0.3s ease;
    flex-grow: 1;
}

/* Specific styles for the PDF iframe */
.pdf-iframe {
    border: none;
    width: 100%;
    height: 600px;
    background: white;
}

.pdf-fallback {
    padding: 2rem;
    text-align: center;
    background-color: var(--bg-primary);
}

.pdf-fallback p {
    margin-bottom: 1rem;
}

.pdf-fallback a {
    color: var(--accent-color);
    text-decoration: underline;
    transition: color 0.2s ease;
}

.pdf-fallback a:hover {
    color: var(--accent-hover);
}

.document-actions {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 1rem;
    padding: 1rem;
    background-color: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    animation: fadeIn 0.6s ease-out;
}

/* Solution Preview */
.solution-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.solution-actions {
    display: flex;
    gap: 1rem;
}

.solution-container {
    margin-bottom: 2rem;
}

.code-container {
    margin-bottom: 1rem;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 3px 10px rgba(0, 0, 0, 0.08);
    transition: box-shadow 0.3s ease;
}

.code-container:hover {
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.12);
}

.code-loaded {
    animation: codeLoaded 0.5s ease-out;
}

@keyframes codeLoaded {
    0% { opacity: 0.5; transform: translateY(10px); }
    100% { opacity: 1; transform: translateY(0); }
}

pre {
    border-radius: 8px;
    overflow: auto;
    max-height: 500px;
    margin: 0;
}

code {
    font-family: 'Consolas', 'Monaco', monospace;
    font-size: 14px;
}

.code-loading {
    padding: 2rem;
    text-align: center;
    color: var(--text-secondary);
}

.output-container {
    margin-top: 1.5rem;
    padding: 1.5rem;
    background-color: var(--bg-primary);
    border-radius: 8px;
    border-left: 4px solid var(--accent-color);
    animation: fadeIn 0.5s ease;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.output-container:hover {
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.08);
    transform: translateY(-2px);
}

.error-container {
    margin-top: 1.5rem;
    padding: 1.5rem;
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--error-color);
    border-radius: 8px;
    border-left: 4px solid var(--error-color);
    animation: fadeIn 0.5s ease;
}

/* Loading and Error States */
.loading {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 2rem;
    color: var(--text-secondary);
    position: relative;
}

.loading::after {
    content: '';
    width: 30px;
    height: 30px;
    border: 3px solid var(--border-color);
    border-radius: 50%;
    border-top-color: var(--accent-color);
    animation: spin 1s infinite linear;
    margin-left: 10px;
}

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

.error-message {
    padding: 1.5rem;
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--error-color);
    border-radius: 8px;
    border-left: 4px solid var(--error-color);
    margin-top: 1rem;
}

.no-assignments {
    padding: 2rem;
    text-align: center;
    color: var(--text-secondary);
}

/* Console Output */
.console-output,
.result-output {
    margin-bottom: 1.5rem;
}

.console-output h4,
.result-output h4 {
    margin-bottom: 0.5rem;
    color: var(--accent-color);
}

.console-output pre,
.result-output pre {
    background-color: rgba(0, 0, 0, 0.05);
    padding: 1rem;
    border-radius: 6px;
    overflow: auto;
    font-family: 'Consolas', 'Monaco', monospace;
}

[data-theme="dark"] .console-output pre,
[data-theme="dark"] .result-output pre {
    background-color: rgba(255, 255, 255, 0.05);
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem;
    background-color: var(--bg-secondary);
    color: var(--text-secondary);
    margin-top: 3rem;
    border-top: 1px solid var(--border-color);
}

footer p {
    transition: transform 0.3s ease;
}

footer a {
    color: var(--accent-color);
    text-decoration: none;
    transition: color 0.2s ease, transform 0.2s ease;
    display: inline-block;
}

footer a:hover {
    color: var(--accent-hover);
    transform: translateY(-2px);
}

.heart {
    color: #e53e3e;
    display: inline-block;
    animation: heartbeat 1.5s infinite;
}

@keyframes heartbeat {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.1); }
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .logo h1 {
        font-size: 1.2rem;
    }
    
    .intro h2 {
        font-size: 2rem;
    }
    
    .assignments-grid {
        grid-template-columns: 1fr;
    }
    
    .tab-content {
        padding: 1.5rem;
    }
    
    .solution-header {
        flex-direction: column;
        align-items: flex-start;
    }
    
    .solution-actions {
        margin-top: 1rem;
    }
    
    .pdf-container iframe,
    .pdf-container object {
        min-height: 400px;
    }
    
    .document-actions {
        flex-direction: column;
    }
}