:root {
            --sidebar-width: 260px;
            --sidebar-collapsed-width: 80px;
            --bg-page: #f0f7ff;
            --bg-card: #ffffff;
            --text-main: #1e293b;
            --border-color: #e2e8f0;
            --input-bg: #ffffff;
            --primary-blue: #2563eb;
        }

        .dark-mode {
            --bg-page: #0f172a;
            --bg-card: #1e293b;
            --text-main: #f1f5f9;
            --border-color: #334155;
            --input-bg: #334155;
        }

        body {
            font-family: 'Inter', system-ui, -apple-system, sans-serif;
            background-color: var(--bg-page);
            color: var(--text-main);
            transition: all 0.3s ease;
            margin: 0;
        }

        .card-custom {
            background-color: var(--bg-card);
            border: 1px solid var(--border-color);
            color: var(--text-main);
        }

        input, select {
            background-color: var(--input-bg) !important;
            color: var(--text-main) !important;
            border: 1px solid var(--border-color) !important;
        }

        #sidebar {
            width: var(--sidebar-collapsed-width);
            background-color: var(--bg-card);
            border-right: 1px solid var(--border-color);
            transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        }
        #sidebar:hover { width: var(--sidebar-width); }
        .nav-text { opacity: 0; transition: opacity 0.2s; white-space: nowrap; }
        #sidebar:hover .nav-text { opacity: 1; }

        .auth-wrapper {
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
        }
        .flip-card-inner {
            position: relative;
            width: 100%;
            max-width: 450px;
            height: 520px;
            transition: transform 0.6s;
            transform-style: preserve-3d;
        }
        .flipped { transform: rotateY(180deg); }
        .auth-card {
            position: absolute;
            width: 100%;
            height: 100%;
            backface-visibility: hidden;
            border-radius: 24px;
            padding: 40px;
            display: flex;
            flex-direction: column;
            justify-content: center;
            box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
        }
        .register-face { transform: rotateY(180deg); }

        #themeToggle {
            position: fixed;
            top: 20px;
            right: 20px;
            z-index: 9999;
            cursor: move;
            touch-action: none;
            width: 56px;
            height: 56px;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 24px;
            background: var(--bg-card);
            color: var(--text-main);
            border-radius: 18px;
            box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.2);
            border: 2px solid var(--primary-blue);
        }

        .modal-overlay {
            position: fixed;
            inset: 0;
            background: rgba(0,0,0,0.6);
            backdrop-filter: blur(4px);
            display: flex;
            align-items: center;
            justify-content: center;
            z-index: 1000;
        }

        .hidden { display: none !important; }