:root {
    --bg-color: #ffffff;
    --text-color: #1a1a1a;
    --primary-color: #007bff;
    --primary-hover: #0056b3;
    --border-color: #ddd;
    --input-bg: #f8f9fa;
    --card-bg: #ffffff;
    --shadow: 0 4px 6px rgba(0,0,0,0.1);
    --header-bg: #fff;
    --footer-bg: #f8f9fa;
}

body.dark-mode {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --primary-color: #4dabf7;
    --primary-hover: #1e88e5;
    --border-color: #444;
    --input-bg: #2a2a2a;
    --card-bg: #1e1e1e;
    --shadow: 0 4px 8px rgba(0,0,0,0.25);
    --header-bg: #1e1e1e;
    --footer-bg: #1a1a1a;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    margin: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    max-width: 960px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* --- Header --- */
.site-header {
    background-color: var(--header-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 10;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}
.site-header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.logo { font-size: 1.75rem; font-weight: bold; text-decoration: none; color: var(--text-color); }
.main-nav ul { list-style: none; margin: 0; padding: 0; display: flex; }
.main-nav .nav-item { position: relative; margin-left: 1.5rem; }
.main-nav .nav-link { text-decoration: none; color: var(--text-color); font-weight: 500; padding: 0.5rem 0; }
.dropdown-menu { display: none; position: absolute; top: 100%; left: 0; background-color: var(--card-bg); border: 1px solid var(--border-color); border-radius: 4px; box-shadow: var(--shadow); padding: 0.5rem 0; min-width: 220px; }
.nav-item:hover .dropdown-menu { display: block; }
.dropdown-menu a { display: block; padding: 0.5rem 1rem; text-decoration: none; color: var(--text-color); }
.dropdown-menu a:hover { background-color: var(--input-bg); }
.header-controls .dark-mode-toggle { background: none; border: 1px solid var(--border-color); color: var(--text-color); cursor: pointer; padding: 8px 12px; border-radius: 50%; font-size: 1.2rem; }

/* --- Main Content & Tool --- */
main { padding: 2rem 0; }
.page-header { text-align: center; margin-bottom: 3rem; }
.page-header h1 { font-size: 3rem; margin-bottom: 0.5rem; }
.page-header p { font-size: 1.2rem; color: #6c757d; }
.content-section { margin-bottom: 3rem; }
.content-section h2 { border-bottom: 1px solid var(--border-color); padding-bottom: 0.5rem; margin-bottom: 1.5rem; }
.tool-container { background-color: var(--card-bg); padding: 2.5rem; border-radius: 8px; box-shadow: var(--shadow); border: 1px solid var(--border-color); }
.control-group { margin-bottom: 1.5rem; }
label { display: block; margin-bottom: 0.5rem; font-weight: 600; font-size: 1.1rem; }
.tool-select { width: 100%; padding: 0.85rem; border: 1px solid var(--border-color); border-radius: 4px; background-color: var(--input-bg); color: var(--text-color); font-size: 1rem; }
.tool-button { width: 100%; padding: 0.85rem; font-size: 1.1rem; font-weight: bold; color: #fff; background-color: var(--primary-color); border: none; border-radius: 4px; cursor: pointer; transition: background-color 0.2s; }
.tool-button:hover:not(:disabled) { background-color: var(--primary-hover); }
.tool-button:disabled { background-color: #888; cursor: not-allowed; opacity: 0.7; }

/* --- Status Messages --- */
.status-message { margin-top: 1rem; padding: 1rem; border-radius: 4px; text-align: center; }
.status-message.success { background-color: #d4edda; color: #155724; }
.status-message.error { background-color: #f8d7da; color: #721c24; }
.status-message.info { background-color: #cce5ff; color: #004085; }
body.dark-mode .status-message.success { background-color: #1d4b29; color: #a3e9b6; }
body.dark-mode .status-message.error { background-color: #5d2227; color: #f8b2b6; }
body.dark-mode .status-message.info { background-color: #0d3c61; color: #9cc2e5; }

/* --- Footer --- */
.site-footer { background-color: var(--footer-bg); padding: 3rem 0; border-top: 1px solid var(--border-color); }
.footer-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 2rem; margin-bottom: 2rem; }
.footer-column h4 { margin-bottom: 1rem; }
.footer-column ul { list-style: none; padding: 0; }
.footer-column ul li { margin-bottom: 0.5rem; }
.footer-column a { text-decoration: none; color: var(--text-color); }
.footer-column a:hover { text-decoration: underline; }
.footer-bottom { text-align: center; padding-top: 2rem; border-top: 1px solid var(--border-color); font-size: 0.9rem; }