:root {
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary: #64748b;
    --bg-body: #f8fafc;
    --bg-paper: #ffffff;
    --text-main: #0f172a;
    --text-muted: #475569;
    --border: #e2e8f0;
    --toolbar-height: 64px;
    --sidebar-width: 220px;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
    --radius: 8px;
}

[data-theme="dark"] {
    --primary: #3b82f6;
    --primary-hover: #60a5fa;
    --bg-body: #0f172a;
    --bg-paper: #1e293b;
    --text-main: #f1f5f9;
    --text-muted: #94a3b8;
    --border: #334155;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background: var(--bg-body);
    color: var(--text-main);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    line-height: 1.6;
    transition: background 0.2s, color 0.2s;
}

h1, h2, h3, h4 { line-height: 1.2; font-weight: 700; color: var(--text-main); }
h1 { font-size: 2.5rem; margin-bottom: 1rem; }
h2 { font-size: 1.8rem; margin-top: 2.5rem; margin-bottom: 1rem; }
h3 { font-size: 1.25rem; margin-bottom: 0.5rem; }
p { margin-bottom: 1rem; color: var(--text-muted); }

a { color: var(--primary); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--primary-hover); text-decoration: underline; }

/* Header */
.app-header {
    background: var(--bg-paper);
    border-bottom: 1px solid var(--border);
    height: var(--toolbar-height);
    display: flex;
    align-items: center;
    padding: 0 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-sm);
}

.logo {
    font-weight: 800;
    font-size: 1.25rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-right: 3rem;
    color: var(--text-main);
}
.logo svg { width: 28px; height: 28px; }

.btn-icon { 
    background: transparent; 
    border: 1px solid var(--border); 
    border-radius: var(--radius); 
    padding: 6px 10px; 
    cursor: pointer; 
    color: var(--text-main);
    transition: all 0.2s;
}
.btn-icon:hover { background: var(--border); }

#mobile-menu-btn { display: none; background: none; border: none; font-size: 1.5rem; cursor: pointer; color: var(--text-main); margin-right: 1rem; }

.main-nav { display: flex; align-items: center; gap: 2rem; }
.main-nav a {
    color: var(--text-muted);
    font-weight: 600;
    font-size: 0.95rem;
    padding: 0.5rem 0;
    border-bottom: 2px solid transparent;
}
.main-nav a:hover, .main-nav a.active { color: var(--primary); border-bottom-color: var(--primary); text-decoration: none; }

.actions { margin-left: auto; display: flex; align-items: center; gap: 1rem; }

/* Upload Zone */
.stage { display: none; width: 100%; flex: 1; }
.stage.active { display: flex; flex-direction: column; }

.upload-zone {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 4rem 2rem;
    text-align: center;
    background: radial-gradient(circle at center, var(--bg-paper) 0%, var(--bg-body) 100%);
}

.upload-box {
    border: 2px dashed var(--border);
    background: var(--bg-paper);
    padding: 5rem;
    border-radius: 1rem;
    margin: 2rem 0;
    transition: all 0.3s ease;
    cursor: pointer;
    box-shadow: var(--shadow-sm);
    max-width: 600px;
    width: 100%;
}

.upload-box:hover, .upload-box.drag-over {
    border-color: var(--primary);
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
    background: rgba(37, 99, 235, 0.02);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    max-width: 1200px;
    width: 100%;
    margin-top: 4rem;
}

.feature-item {
    background: var(--bg-paper);
    padding: 2rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    text-align: left;
    transition: transform 0.2s;
    box-shadow: var(--shadow-sm);
}
.feature-item:hover { transform: translateY(-2px); border-color: var(--primary); }

/* Workspace Toolbar */
.toolbar {
    background: var(--bg-paper);
    border-bottom: 1px solid var(--border);
    padding: 0.75rem 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    flex-wrap: wrap;
    position: sticky;
    top: var(--toolbar-height);
    z-index: 90;
    box-shadow: var(--shadow-sm);
}

.tool-group { display: flex; gap: 0.25rem; align-items: center; background: var(--bg-body); padding: 4px; border-radius: 6px; border: 1px solid var(--border); }
.tool-separator { width: 1px; height: 24px; background: var(--border); margin: 0 0.25rem; }

.tool-btn {
    background: transparent;
    border: none;
    padding: 0.5rem 0.75rem;
    border-radius: 4px;
    cursor: pointer;
    color: var(--text-muted);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.9rem;
    font-weight: 500;
    white-space: nowrap;
    transition: all 0.15s;
}

.tool-btn:hover { background: rgba(0,0,0,0.05); color: var(--text-main); }
.tool-btn.active { background: white; color: var(--primary); box-shadow: 0 1px 2px rgba(0,0,0,0.1); }
[data-theme="dark"] .tool-btn.active { background: #334155; color: white; }

/* Editor Layout */
.editor-layout {
    flex: 1;
    display: flex;
    overflow: hidden;
    height: calc(100vh - var(--toolbar-height) - 60px); /* Approx toolbar height */
}

.thumbnails {
    width: var(--sidebar-width);
    background: var(--bg-paper);
    border-right: 1px solid var(--border);
    overflow-y: auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    flex-shrink: 0;
}

.thumb-item {
    border: 2px solid transparent;
    cursor: pointer;
    border-radius: 6px;
    overflow: hidden;
    aspect-ratio: 1/1.414;
    background: var(--bg-body);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    color: var(--secondary);
    font-size: 1.2rem;
    transition: all 0.2s;
    box-shadow: var(--shadow-sm);
    position: relative;
}
.thumb-item::after { content: attr(data-page); position: absolute; bottom: 5px; font-size: 0.8rem; }
.thumb-item:hover { border-color: var(--border); transform: scale(1.02); }
.thumb-item.active { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1); }

.viewport {
    flex: 1;
    background: #e5e7eb;
    overflow: auto;
    display: flex;
    justify-content: center;
    padding: 3rem;
    position: relative;
}
[data-theme="dark"] .viewport { background: #020617; }

.pdf-page {
    position: relative;
    background: white;
    margin-bottom: 3rem;
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    transform-origin: top center;
    transition: transform 0.1s;
}

.pdf-text-span {
    position: absolute;
    white-space: pre;
    cursor: text;
    line-height: 1;
    transform-origin: 0% 0%;
    padding: 2px 1px;
    border-radius: 2px;
    border: 1px solid transparent;
}
.pdf-text-span:hover { background: rgba(37, 99, 235, 0.1); outline: 1px dashed var(--primary); }
.pdf-text-span:focus { background: white; outline: 2px solid var(--primary); z-index: 20; box-shadow: 0 4px 12px rgba(0,0,0,0.15); }
.pdf-text-span.selected-block { outline: 2px solid var(--primary); z-index: 10; background: rgba(37, 99, 235, 0.05); }

/* Buttons */
.btn {
    padding: 0.6rem 1.25rem;
    border-radius: 6px;
    font-weight: 600;
    border: none;
    cursor: pointer;
    transition: all 0.2s;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}
.btn-primary { background: var(--primary); color: white; box-shadow: 0 1px 2px rgba(0,0,0,0.1); }
.btn-primary:hover { background: var(--primary-hover); transform: translateY(-1px); box-shadow: 0 4px 6px rgba(0,0,0,0.1); }
.btn-secondary { background: transparent; border: 1px solid var(--border); color: var(--text-main); }
.btn-secondary:hover { background: var(--bg-body); border-color: var(--text-muted); }
.btn-lg { padding: 0.875rem 2rem; font-size: 1.125rem; }

/* SEO Content Area */
.seo-content {
    background: var(--bg-paper);
    padding: 4rem 0;
    border-top: 1px solid var(--border);
}
.container { max-width: 1000px; margin: 0 auto; padding: 0 2rem; }
.seo-content ul { padding-left: 1.5rem; margin-bottom: 1.5rem; color: var(--text-muted); }
.seo-content li { margin-bottom: 0.5rem; }

/* Footer */
footer {
    background: var(--bg-body);
    border-top: 1px solid var(--border);
    padding: 3rem 0;
    margin-top: auto;
}
.footer-links { display: flex; gap: 2rem; justify-content: center; margin-bottom: 1.5rem; flex-wrap: wrap; }
.footer-links a { color: var(--text-muted); font-weight: 500; }
footer p { text-align: center; font-size: 0.9rem; }

/* Mobile Menu & Responsive */
@media (max-width: 768px) {
    .app-header { padding: 0 1rem; }
    .logo span { display: none; }
    .features-grid { grid-template-columns: 1fr; }
    .thumbnails { display: none; }
    .editor-layout { flex-direction: column; }
    
    #mobile-menu-btn { display: block; z-index: 102; }
    
    .main-nav { 
        position: fixed; 
        top: var(--toolbar-height); 
        left: 0; right: 0; bottom: 0;
        background: var(--bg-paper);
        flex-direction: column; 
        align-items: flex-start;
        padding: 2rem;
        gap: 1.5rem;
        transform: translateX(100%);
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        z-index: 101;
        border-top: 1px solid var(--border);
    }
    .main-nav.active { transform: translateX(0); }
    .main-nav a { font-size: 1.2rem; width: 100%; border-bottom: 1px solid var(--border); }
    
    .toolbar { overflow-x: auto; padding: 0.5rem; gap: 0.5rem; justify-content: flex-start; }
    .tool-group { flex-shrink: 0; }
    
    .viewport { padding: 1rem; }
}

.hidden { display: none !important; }