:root {
    --primary-color: #007bff;
    --primary-dark: #0056b3;
    --text-primary: #212529;
    --text-secondary: #6c757d;
    --bg-primary: #ffffff;
    --bg-secondary: #f8f9fa;
    --border-color: #dee2e6;
    --danger-color: #dc3545;
    --success-color: #28a745;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --font-size-base: 16px;
    --line-height-base: 1.6;
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --border-radius: 0.375rem;
    --transition-speed: 0.2s;
}
body.high-contrast {
    --primary-color: #0000ff;
    --text-primary: #000000;
    --text-secondary: #000000;
    --bg-primary: #ffffff;
    --bg-secondary: #ffffff;
    --border-color: #000000;
    --danger-color: #cc0000;
    --success-color: #006600;
}
body.large-font { --font-size-base: 20px; }
*, *::before, *::after { box-sizing: border-box; }
body {
    margin: 0;
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    color: var(--text-primary);
    background-color: var(--bg-secondary);
}
.hidden { display: none !important; }
.visually-hidden {
    position: absolute; width: 1px; height: 1px;
    padding: 0; margin: -1px; overflow: hidden;
    clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0;
}
.container { max-width: 1200px; margin: 0 auto; padding: 0 var(--spacing-md); }

/* Header */
header {
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    position: sticky; top: 0; z-index: 50;
}
.nav-container {
    display: flex; align-items: center; justify-content: space-between;
    padding: var(--spacing-md); max-width: 1200px; margin: 0 auto; gap: var(--spacing-lg);
}
.logo { margin: 0; font-size: 1.5rem; }
.logo a {
    display: flex; align-items: center; gap: var(--spacing-sm);
    text-decoration: none; color: var(--text-primary);
    transition: color var(--transition-speed);
}
.logo a:hover, .logo a:focus {
    color: var(--primary-color);
    outline: 2px solid var(--primary-color); outline-offset: 2px;
}

/* Dropdown nav */
.dropdown { position: relative; }
.dropdown-toggle {
    background: transparent; color: var(--text-primary);
    display: flex; align-items: center; gap: var(--spacing-xs);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: var(--spacing-sm) var(--spacing-md);
}
.dropdown-toggle:hover, .dropdown-toggle:focus {
    background: var(--bg-secondary);
    outline: 2px solid var(--primary-color); outline-offset: 2px;
}
.dropdown-toggle[aria-expanded="true"] { background: var(--bg-secondary); }
.dropdown-menu {
    display: none; position: absolute; top: 100%; right: 0;
    background: var(--bg-primary); border: 1px solid var(--border-color);
    border-radius: var(--border-radius); padding: 0;
    margin: var(--spacing-xs) 0 0 0;
    min-width: 180px; list-style: none;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    z-index: 100;
}
.dropdown-menu.show { display: block; }
.dropdown-menu a {
    display: block; padding: var(--spacing-sm) var(--spacing-md);
    text-decoration: none; color: var(--text-primary);
    transition: background-color var(--transition-speed);
}
.dropdown-menu a:hover, .dropdown-menu a:focus {
    background: var(--bg-secondary);
    outline: 2px solid var(--primary-color); outline-offset: -2px;
}
.menu-sep { height: 1px; background: var(--border-color); margin: var(--spacing-xs) 0; }
.menu-stat { padding: var(--spacing-xs) var(--spacing-md); font-size: 0.85rem; color: var(--text-secondary); }
.menu-label { padding: var(--spacing-xs) var(--spacing-md); font-size: 0.75rem; color: var(--text-secondary); text-transform: uppercase; letter-spacing: 0.05em; }
.menu-toggle {
    display: block; width: 100%; text-align: left;
    background: transparent; color: var(--text-primary);
    padding: var(--spacing-sm) var(--spacing-md);
    border: none; border-radius: var(--border-radius);
    font-size: inherit; cursor: pointer;
}
.menu-toggle:hover, .menu-toggle:focus {
    background: var(--bg-secondary);
    outline: 2px solid var(--primary-color); outline-offset: -2px;
}
.menu-toggle[aria-pressed="true"] { color: var(--primary-color); font-weight: 600; }
.menu-about-btn[aria-expanded="true"] { color: var(--primary-color); font-weight: 600; }
.menu-about-text { padding: var(--spacing-xs) var(--spacing-md) var(--spacing-sm); font-size: 0.8rem; color: var(--text-secondary); line-height: 1.5; }
.menu-about-text[hidden] { display: none; }

/* Nav actions */
.nav-actions { display: flex; gap: var(--spacing-sm); align-items: center; }
.nav-user { font-size: 0.9rem; color: var(--text-secondary); }

/* Search bar */
.search-bar { background: var(--bg-primary); border-bottom: 1px solid var(--border-color); padding: var(--spacing-sm) 0; }
.search-bar .container { display: flex; gap: var(--spacing-sm); }
.search-bar input { flex: 1; }

/* Buttons */
button {
    font-family: inherit; font-size: inherit;
    cursor: pointer; border: none; border-radius: var(--border-radius);
    padding: var(--spacing-sm) var(--spacing-md);
    transition: all var(--transition-speed);
}
button:focus { outline: 2px solid var(--primary-color); outline-offset: 2px; }
button:disabled { opacity: 0.5; cursor: not-allowed; }
.btn-primary { background: var(--primary-color); color: white; }
.btn-primary:hover:not(:disabled) { background: var(--primary-dark); }
.btn-text { background: transparent; color: var(--text-primary); }
.btn-text:hover { background: var(--bg-secondary); }
.btn-link { background: transparent; color: var(--primary-color); padding: 0; text-decoration: underline; font-size: inherit; }
.btn-block { width: 100%; }

/* Announcements */
.announcements { background: var(--bg-primary); padding: var(--spacing-lg) 0; }
.alert { padding: var(--spacing-md); border-radius: var(--border-radius); border-left: 4px solid; }
.alert-info { background: #d1ecf1; border-color: #0c5460; color: #0c5460; }

/* Topics */
.topics-section { padding: var(--spacing-xl) 0; }
.section-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: var(--spacing-lg); }
.section-header h2 { margin: 0; font-size: 1.75rem; }
.topics-list { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: var(--spacing-sm); }
.topic-card { background: var(--bg-primary); border: 1px solid var(--border-color); border-radius: var(--border-radius); }
.topic-main { display: flex; align-items: center; }
.topic-link {
    flex: 1; display: block; text-decoration: none; color: inherit;
    padding: var(--spacing-md) var(--spacing-lg);
    transition: background-color var(--transition-speed);
    border-radius: var(--border-radius); min-width: 0;
}
.topic-link:hover, .topic-link:focus { background: var(--bg-secondary); outline: 2px solid var(--primary-color); outline-offset: -2px; }
.topic-row { display: flex; flex-direction: column; gap: var(--spacing-xs); min-width: 0; }
.topic-title { font-weight: 600; font-size: 1.05rem; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; color: var(--text-primary); }
.topic-meta { font-size: 0.8rem; color: var(--text-secondary); display: flex; gap: var(--spacing-xs); align-items: center; white-space: nowrap; flex-wrap: wrap; }
.meta-author { font-weight: 500; }
.meta-dot { opacity: 0.5; }
.meta-replies { color: var(--primary-color); }
.meta-views { opacity: 0.7; }
.topic-category-tag { font-size: 0.7rem; padding: 1px 6px; border-radius: 10px; background: var(--bg-secondary); color: var(--text-secondary); margin-left: var(--spacing-xs); }

/* Topic action select */
.topic-action-select {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color); border-radius: var(--border-radius);
    background: var(--bg-primary); font-size: inherit; cursor: pointer;
    flex-shrink: 0; margin-right: var(--spacing-sm);
}
.topic-action-select:focus { outline: 2px solid var(--primary-color); outline-offset: 2px; }

/* Pagination */
.pagination { display: flex; justify-content: center; margin-top: var(--spacing-lg); }
#page-select, .topic-action-select {
    padding: var(--spacing-sm) var(--spacing-md); border: 1px solid var(--border-color);
    border-radius: var(--border-radius); background: var(--bg-primary); font-size: inherit; cursor: pointer;
}
#page-select:focus { outline: 2px solid var(--primary-color); outline-offset: 2px; }

/* Profile */
.profile-section { padding: var(--spacing-xl) 0; }
.profile-card { display: flex; gap: var(--spacing-md); align-items: center; background: var(--bg-primary); border: 1px solid var(--border-color); border-radius: var(--border-radius); padding: var(--spacing-lg); margin-bottom: var(--spacing-lg); }
.profile-avatar { width: 64px; height: 64px; border-radius: 50%; background: var(--primary-color); flex-shrink: 0; }
.profile-name { font-size: 1.3rem; font-weight: 600; margin: 0 0 var(--spacing-xs) 0; }
.profile-bio { color: var(--text-secondary); margin: 0; }

/* Footer */
footer { background: var(--text-primary); color: white; padding: var(--spacing-lg) 0; }
.footer-content { text-align: center; }

/* Modal */
.modal-overlay {
    position: fixed; inset: 0; background: rgba(0,0,0,0.5);
    display: flex; align-items: flex-start; justify-content: center;
    padding: var(--spacing-lg); overflow-y: auto; z-index: 200;
}
.modal {
    background: var(--bg-primary); border-radius: var(--border-radius);
    padding: var(--spacing-xl); max-width: 500px; width: 100%;
    margin-top: 5vh; box-shadow: 0 8px 32px rgba(0,0,0,0.2);
    position: relative;
}
.modal-large { max-width: 700px; }
.modal-close {
    position: absolute; top: var(--spacing-sm); right: var(--spacing-sm);
    background: transparent; font-size: 1.5rem; line-height: 1;
    padding: var(--spacing-xs) var(--spacing-sm); color: var(--text-secondary);
}
.modal-close:hover, .modal-close:focus { color: var(--text-primary); }
.modal h2 { margin-top: 0; }

/* Forms */
.form-group { margin-bottom: var(--spacing-md); }
.form-group label { display: block; margin-bottom: var(--spacing-xs); font-weight: 500; }
.form-group input, .form-group select, .form-group textarea {
    width: 100%; padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color); border-radius: var(--border-radius);
    font-family: inherit; font-size: inherit; background: var(--bg-primary); color: var(--text-primary);
}
.form-group input:focus, .form-group select:focus, .form-group textarea:focus {
    outline: 2px solid var(--primary-color); outline-offset: -1px; border-color: var(--primary-color);
}
.form-error { color: var(--danger-color); font-size: 0.85rem; min-height: 1em; margin-bottom: var(--spacing-sm); }
.form-footer { text-align: center; margin-top: var(--spacing-md); color: var(--text-secondary); font-size: 0.9rem; }

/* Detail */
.detail-meta { color: var(--text-secondary); font-size: 0.85rem; margin-bottom: var(--spacing-md); }
.detail-content { margin-bottom: var(--spacing-lg); line-height: 1.8; }
.detail-replies-heading { font-size: 1.1rem; margin-bottom: var(--spacing-md); }
.replies-list { list-style: none; padding: 0; margin: 0 0 var(--spacing-lg) 0; display: flex; flex-direction: column; gap: var(--spacing-sm); }
.reply-item { background: var(--bg-secondary); border-radius: var(--border-radius); padding: var(--spacing-md); }
.reply-author { font-weight: 600; font-size: 0.9rem; }
.reply-time { color: var(--text-secondary); font-size: 0.75rem; margin-left: var(--spacing-xs); }
.reply-text { margin-top: var(--spacing-xs); }
.reply-form { display: flex; flex-direction: column; gap: var(--spacing-sm); }
.reply-form textarea { width: 100%; padding: var(--spacing-sm) var(--spacing-md); border: 1px solid var(--border-color); border-radius: var(--border-radius); font-family: inherit; font-size: inherit; resize: vertical; }
.reply-form textarea:focus { outline: 2px solid var(--primary-color); outline-offset: -1px; border-color: var(--primary-color); }
.reply-form button { align-self: flex-start; }

/* Responsive */
@media (max-width: 768px) {
    .nav-container { flex-wrap: wrap; }
    .modal { padding: var(--spacing-md); margin-top: 2vh; }
    .section-header { flex-direction: column; gap: var(--spacing-sm); align-items: flex-start; }
    .topic-main { flex-direction: column; align-items: stretch; }
    .topic-action-select { margin: 0 var(--spacing-sm) var(--spacing-sm); }
    .profile-card { flex-direction: column; text-align: center; }
}
@media (prefers-reduced-motion: reduce) {
    * { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
}