:root {
            --bg-color: #0d1117;
            --panel-bg: #161b22;
            --text-main: #c9d1d9;
            --accent-green: #3fb950;
            --accent-green-hover: #2ea043;
            --accent-red: #f85149;
            --accent-blue: #58a6ff;
            --border-color: #30363d;
            --terminal-bg: #010409;
        }

        body {
            background-color: var(--bg-color);
            color: var(--text-main);
            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
            margin: 0;
            padding: 0;
            display: flex;
            flex-direction: column;
            min-height: 100vh;
            overflow-x: hidden;
        }

        header {
            background-color: var(--panel-bg);
            padding: 1rem 2rem;
            border-bottom: 1px solid var(--border-color);
            display: flex;
            justify-content: space-between;
            align-items: center;
            box-shadow: 0 4px 6px rgba(0,0,0,0.3);
            position: sticky;
            top: 0;
            z-index: 100;
            flex-wrap: wrap;
            gap: 1rem;
        }

        header h1 {
            margin: 0;
            font-size: 1.4rem;
            color: var(--accent-green);
            font-family: 'Courier New', Courier, monospace;
            text-shadow: 0 0 8px rgba(63, 185, 80, 0.4);
            letter-spacing: 1px;
        }

        nav { display: flex; gap: 1.5rem; align-items: center; flex-wrap: wrap; }
        nav a {
            color: var(--text-main);
            text-decoration: none;
            font-weight: 600;
            transition: color 0.2s ease-in-out;
            font-size: 0.95rem;
            cursor: pointer;
        }
        nav a:hover, nav a.active { color: var(--accent-green); }

        main {
            flex: 1;
            padding: 2.5rem 2rem;
            max-width: 1400px;
            margin: 0 auto;
            width: 100%;
            box-sizing: border-box;
        }

        .main-grid {
            display: grid;
            grid-template-columns: 280px 1fr;
            gap: 2.5rem;
            align-items: start;
        }

        .standalone-view {
            max-width: 800px;
            margin: 0 auto;
            animation: fadeIn 0.3s ease-out;
        }

        @media (max-width: 900px) {
            .main-grid {
                grid-template-columns: 1fr;
                padding: 0;
                gap: 1.5rem;
            }
            main { padding: 1.5rem 1rem; }
            .sidebar { display: flex; flex-wrap: wrap; gap: 0.5rem; }
            .sidebar h2 { width: 100%; margin-bottom: 0.5rem; }
            .category-btn { width: auto; flex: 1 1 calc(50% - 0.5rem); text-align: center; border-left: none; border-bottom: 3px solid transparent; }
            .category-btn.active { border-left: none; border-bottom: 3px solid var(--accent-green); }
        }

        @media (max-width: 600px) {
            header { flex-direction: column; gap: 1rem; padding: 1rem; }
            nav { flex-wrap: wrap; justify-content: center; gap: 1rem; }
            .category-btn { flex: 1 1 100%; }
            .terminal { padding: 1rem; font-size: 0.85rem; }
            .flag-form { flex-direction: column; }
            .submit-btn { width: 100%; }
        }

        .sidebar {
            background-color: var(--panel-bg);
            border: 1px solid var(--border-color);
            border-radius: 8px;
            padding: 1.2rem;
            box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }

        .sidebar h2 {
            font-size: 1.1rem;
            border-bottom: 1px solid var(--border-color);
            padding-bottom: 0.8rem;
            margin-top: 0;
            color: #8b949e;
            text-transform: uppercase;
            letter-spacing: 1px;
        }

        .category-btn {
            display: block; width: 100%; background: none; border: none;
            color: var(--text-main); text-align: left; padding: 0.8rem 1rem;
            margin-bottom: 0.5rem; cursor: pointer; font-family: inherit;
            font-size: 0.95rem; font-weight: 500; border-radius: 6px;
            transition: all 0.2s ease; border-left: 3px solid transparent;
        }
        .category-btn:hover { background-color: rgba(139, 148, 158, 0.1); }
        .category-btn.active {
            background-color: rgba(63, 185, 80, 0.1);
            color: var(--accent-green);
            border-left: 3px solid var(--accent-green);
        }

        .content-area { display: flex; flex-direction: column; gap: 1.5rem; }

        .chall-card {
            background-color: var(--panel-bg); border: 1px solid var(--border-color);
            border-radius: 8px; padding: 2rem; box-shadow: 0 4px 12px rgba(0,0,0,0.15);
            animation: fadeIn 0.3s ease-out;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .chall-card h2 {
            margin-top: 0; color: #fff; display: flex; align-items: center;
            font-size: 1.3rem; padding-bottom: 1rem; border-bottom: 1px solid var(--border-color);
            flex-wrap: wrap; gap: 10px;
        }

        .pts-badge {
            background-color: rgba(63, 185, 80, 0.15); padding: 0.3rem 0.8rem;
            border-radius: 20px; font-size: 0.85rem; color: var(--accent-green);
            border: 1px solid rgba(63, 185, 80, 0.3); font-weight: 600; white-space: nowrap;
        }

        .help-flag-btn {
            background: rgba(255, 255, 255, 0.05); border: 1px solid var(--border-color);
            border-radius: 6px; cursor: pointer; font-size: 1.2rem; padding: 4px 10px;
            transition: all 0.2s; margin-left: auto; display: flex; align-items: center; gap: 6px;
            color: var(--text-main); font-family: inherit; font-size: 0.85rem; font-weight: 600;
        }
        .help-flag-btn:hover { background: rgba(255, 255, 255, 0.15); border-color: #fff; }

        .hint-box {
            background-color: rgba(255, 255, 255, 0.05); border-left: 4px solid #fff;
            padding: 1.5rem; margin: 1rem 0 1.5rem 0; border-radius: 0 6px 6px 0;
            line-height: 1.6; animation: fadeIn 0.3s ease;
        }
        .hint-box h4 { margin: 0 0 1rem 0; color: #fff; display: flex; align-items: center; gap: 8px; }
        .hint-box ul { margin: 0; padding-left: 1.5rem; }
        .hint-box li { margin-bottom: 0.5rem; }

        .analogy-box {
            background-color: rgba(139, 148, 158, 0.1); border-left: 4px solid #8b949e;
            padding: 1.2rem; margin: 1.5rem 0; border-radius: 0 6px 6px 0; line-height: 1.5;
        }
        .analogy-box h4 { margin: 0 0 0.5rem 0; color: #c9d1d9; }
        
        .scenario-box {
            background-color: rgba(88, 166, 255, 0.05); border: 1px dashed var(--accent-blue);
            padding: 1rem; border-radius: 6px; margin-bottom: 1.5rem;
        }

        .terminal {
            background-color: var(--terminal-bg); border: 1px solid var(--border-color);
            border-radius: 8px; padding: 1.5rem; font-family: 'SFMono-Regular', Consolas, monospace;
            overflow-x: auto; position: relative; box-shadow: inset 0 0 10px rgba(0,0,0,0.5);
            margin-bottom: 1.5rem; font-size: 0.95rem; line-height: 1.6;
        }

        .terminal-header {
            position: absolute; top: 0; left: 0; right: 0; background: #21262d;
            padding: 6px 12px; font-size: 0.8rem; color: #8b949e; border-radius: 8px 8px 0 0;
            display: flex; gap: 6px; align-items: center; border-bottom: 1px solid var(--border-color);
        }
        
        .terminal-dot { width: 12px; height: 12px; border-radius: 50%; display: inline-block; }
        .dot-red { background: #ff5f56; } .dot-yellow { background: #ffbd2e; } .dot-green { background: #27c93f; }

        .terminal-content { margin-top: 20px; color: #e6edf3; }
        .prompt { color: var(--accent-green); font-weight: bold; }
        
        .input-line { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 5px; align-items: center; }
        .term-input {
            background: transparent; border: none; color: #fff; font-family: inherit; font-size: inherit;
            flex: 1 1 200px; outline: none; caret-color: var(--accent-green);
        }
        .term-input::placeholder { color: #484f58; }
        
        .output-line { color: #8b949e; margin-top: 8px; white-space: pre-wrap; word-break: break-all; }
        .success-flag { color: #e3b341; font-weight: bold; display: block; margin-top: 5px; }
        .error-text { color: #f85149; margin-top: 5px; display: block;}

        .tool-input {
            width: 100%; padding: 8px; background: #161b22; border: 1px solid #30363d;
            color: #c9d1d9; border-radius: 4px; font-family: monospace; margin-bottom: 10px; box-sizing: border-box;
        }
        .tool-btn {
            background: #238636; color: white; border: none; padding: 8px 16px; border-radius: 4px;
            cursor: pointer; font-weight: bold; width: 100%; transition: 0.2s;
        }
        .tool-btn:hover { background: #2ea043; }

        .flag-form {
            display: flex; gap: 10px; margin-top: 1.5rem; padding-top: 1.5rem; border-top: 1px solid var(--border-color);
        }
        .flag-input {
            flex: 1; padding: 0.8rem 1rem; background-color: var(--bg-color); border: 1px solid var(--border-color);
            border-radius: 6px; color: var(--text-main); font-family: 'SFMono-Regular', Consolas, monospace;
            font-size: 1rem; transition: border-color 0.2s;
        }
        .flag-input:focus { border-color: var(--accent-green); outline: none; box-shadow: 0 0 0 3px rgba(63, 185, 80, 0.15); }
        
        .submit-btn {
            background-color: var(--panel-bg); color: var(--accent-green); border: 1px solid var(--border-color);
            padding: 0.8rem 1.5rem; border-radius: 6px; cursor: pointer; font-weight: 600; font-family: inherit;
            font-size: 1rem; transition: all 0.2s;
        }
        .submit-btn:hover { background-color: var(--accent-green); color: #ffffff; border-color: var(--accent-green); }

        .status-msg { margin-top: 12px; font-size: 0.95rem; font-weight: 500; padding: 0.8rem; border-radius: 6px; display: none; }
        .status-correct { background-color: rgba(63, 185, 80, 0.1); color: var(--accent-green); border: 1px solid rgba(63, 185, 80, 0.2); display: block; }
        .status-wrong { background-color: rgba(248, 81, 73, 0.1); color: var(--accent-red); border: 1px solid rgba(248, 81, 73, 0.2); display: block; }

        .hidden { display: none !important; }
        code { background-color: rgba(139, 148, 158, 0.15); padding: 2px 6px; border-radius: 4px; font-family: monospace; color: #a5d6ff;}

        .login-container {
            max-width: 400px; margin: 4rem auto; background-color: var(--panel-bg);
            border: 1px solid var(--border-color); border-radius: 8px; padding: 2rem;
            box-shadow: 0 4px 12px rgba(0,0,0,0.15); text-align: center;
        }
        .login-input {
            width: 100%; padding: 0.8rem; margin: 0.8rem 0; background: var(--bg-color);
            border: 1px solid var(--border-color); border-radius: 4px; color: var(--text-main);
            box-sizing: border-box; font-family: inherit; font-size: 1rem;
        }
        .login-input:focus { border-color: var(--accent-green); outline: none; }
        
        .scoreboard-table {
            width: 100%; border-collapse: collapse; margin-top: 1rem;
        }
        .scoreboard-table th, .scoreboard-table td {
            padding: 1rem; text-align: left; border-bottom: 1px solid var(--border-color);
        }
        .scoreboard-table th { color: var(--accent-green); font-weight: bold; background: #21262d; }
        .scoreboard-table tr:hover { background-color: rgba(255,255,255,0.05); }
        .rank-1 { color: #ffd700; font-weight: bold; font-size: 1.2rem; }
        .rank-2 { color: #c0c0c0; font-weight: bold; font-size: 1.1rem; }
        .rank-3 { color: #cd7f32; font-weight: bold; font-size: 1.05rem; }
        
        .solved-overlay {
            background-color: rgba(63, 185, 80, 0.1); border: 1px dashed var(--accent-green);
            padding: 1.5rem; border-radius: 6px; color: var(--accent-green); font-weight: bold;
            text-align: center; margin-top: 1.5rem; display: none; font-size: 1.2rem;
        }
        
        .user-profile {
            display: flex; align-items: center; gap: 1rem; font-size: 0.9rem; margin-left: 1rem;
            padding-left: 1rem; border-left: 1px solid var(--border-color);
        }
        .logout-btn {
            background: transparent; border: 1px solid var(--accent-red); color: var(--accent-red);
            padding: 4px 12px; border-radius: 4px; cursor: pointer; transition: 0.2s; font-weight:bold;
        }
        .logout-btn:hover { background: var(--accent-red); color: white; }
        
        @media (max-width: 600px) {
            .user-profile { border-left: none; padding-left: 0; margin-left: 0; width: 100%; justify-content: center; margin-top: 10px; }
        }

        #conn-status { font-size: 0.75rem; font-weight: bold; background: rgba(255,255,255,0.1); padding: 4px 8px; border-radius: 12px; display: flex; align-items: center; gap: 5px; }
        .conn-offline { color: #f85149; }
        .conn-online { color: #3fb950; }