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

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
            min-height: 100vh;
            padding: 20px;
        }

        .container {
            max-width: 1400px;
            margin: 0 auto;
            background: white;
            border-radius: 20px;
            box-shadow: 0 20px 60px rgba(0,0,0,0.3);
            overflow: hidden;
        }

        header {
            background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
            color: white;
            padding: 30px;
            text-align: center;
        }

        header h1 {
            font-size: 2.5em;
            margin-bottom: 10px;
            text-shadow: 2px 2px 4px rgba(0,0,0,0.2);
        }

        header p {
            font-size: 1.2em;
            opacity: 0.9;
        }

        nav {
            background: #f8f9fa;
            padding: 15px;
            display: flex;
            justify-content: center;
            gap: 10px;
            flex-wrap: wrap;
            border-bottom: 3px solid #2a5298;
        }

        .nav-btn {
            padding: 12px 24px;
            background: white;
            border: 2px solid #2a5298;
            color: #2a5298;
            border-radius: 25px;
            cursor: pointer;
            font-weight: bold;
            transition: all 0.3s;
            font-size: 1em;
        }

        .nav-btn:hover, .nav-btn.active {
            background: #2a5298;
            color: white;
            transform: translateY(-2px);
            box-shadow: 0 5px 15px rgba(42, 82, 152, 0.3);
        }

        .content {
            padding: 30px;
        }

        .section {
            display: none;
        }

        .section.active {
            display: block;
            animation: fadeIn 0.5s;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(20px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .calculator-grid {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 30px;
            margin-top: 20px;
        }

        @media (max-width: 968px) {
            .calculator-grid {
                grid-template-columns: 1fr;
            }
        }

        .card {
            background: #f8f9fa;
            padding: 25px;
            border-radius: 15px;
            box-shadow: 0 5px 15px rgba(0,0,0,0.1);
        }

        .card h2 {
            color: #2a5298;
            margin-bottom: 20px;
            font-size: 1.8em;
            border-bottom: 3px solid #2a5298;
            padding-bottom: 10px;
        }

        .form-group {
            margin-bottom: 20px;
        }

        label {
            display: block;
            margin-bottom: 8px;
            font-weight: bold;
            color: #333;
        }

        input[type="number"] {
            width: 100%;
            padding: 12px;
            border: 2px solid #ddd;
            border-radius: 8px;
            font-size: 1em;
            transition: border-color 0.3s;
        }

        input[type="number"]:focus {
            outline: none;
            border-color: #2a5298;
        }

        .input-group {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 15px;
        }

        button {
            width: 100%;
            padding: 15px;
            background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
            color: white;
            border: none;
            border-radius: 10px;
            font-size: 1.1em;
            font-weight: bold;
            cursor: pointer;
            transition: transform 0.3s, box-shadow 0.3s;
            margin-top: 10px;
        }

        button:hover {
            transform: translateY(-3px);
            box-shadow: 0 10px 25px rgba(42, 82, 152, 0.4);
        }

        button:active {
            transform: translateY(-1px);
        }

        .result {
            background: white;
            padding: 20px;
            border-radius: 10px;
            margin-top: 20px;
            border-left: 5px solid #2a5298;
        }

        .result h3 {
            color: #2a5298;
            margin-bottom: 15px;
            font-size: 1.5em;
        }

        .result-item {
            padding: 10px;
            margin: 10px 0;
            background: #f8f9fa;
            border-radius: 8px;
            font-size: 1.1em;
        }

        .result-item strong {
            color: #1e3c72;
        }

        canvas {
            max-width: 100%;
            height: 400px !important;
            margin-top: 20px;
            background: white;
            border-radius: 10px;
            padding: 10px;
        }

        .theory-content {
            line-height: 1.8;
            color: #333;
        }

        .theory-content h3 {
            color: #2a5298;
            margin-top: 25px;
            margin-bottom: 15px;
            font-size: 1.6em;
        }

        .theory-content ul {
            margin-left: 30px;
            margin-top: 10px;
        }

        .theory-content li {
            margin-bottom: 10px;
        }

        .formula {
            background: #f0f0f0;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
            font-family: 'Courier New', monospace;
            font-size: 1.2em;
            text-align: center;
            border-left: 4px solid #2a5298;
        }

        .app-card {
            background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
            color: white;
            padding: 20px;
            border-radius: 10px;
            margin: 15px 0;
        }

        .app-card h4 {
            font-size: 1.4em;
            margin-bottom: 10px;
        }

        .select-group {
            margin-bottom: 15px;
        }

        select {
            width: 100%;
            padding: 12px;
            border: 2px solid #ddd;
            border-radius: 8px;
            font-size: 1em;
            background: white;
        }

        .info-box {
            background: #e3f2fd;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
            border-left: 4px solid #2196f3;
        }

        .warning-box {
            background: #fff3cd;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
            border-left: 4px solid #ffc107;
        }

        footer {
            background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
            color: white;
            padding: 40px 30px;
            margin-top: 30px;
        }

        .footer-content {
            max-width: 1400px;
            margin: 0 auto;
            display: grid;
            grid-template-columns: 1fr auto 1fr;
            align-items: center;
            gap: 30px;
        }

        .footer-left {
            text-align: left;
        }

        .footer-left h3 {
            font-size: 1.1em;
            margin-bottom: 10px;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .footer-left p {
            margin: 5px 0;
            font-size: 0.95em;
            line-height: 1.6;
        }

        .footer-center {
            text-align: center;
            background: rgba(255, 255, 255, 0.15);
            padding: 20px 30px;
            border-radius: 15px;
            backdrop-filter: blur(10px);
        }

        .footer-center h2 {
            font-size: 1.3em;
            margin-bottom: 5px;
        }

        .footer-right {
            text-align: right;
        }

        .footer-right p {
            margin: 5px 0;
            font-size: 0.95em;
        }

        .footer-subtitle {
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 8px;
            margin-top: 15px;
            font-size: 1em;
            font-weight: 500;
        }

        @media (max-width: 968px) {
            .footer-content {
                grid-template-columns: 1fr;
                text-align: center;
            }
            .footer-left, .footer-right {
                text-align: center;
            }
            .footer-left h3 {
                justify-content: center;
            }
        }

        .slope-indicator {
            display: inline-block;
            padding: 8px 16px;
            border-radius: 20px;
            font-weight: bold;
            margin: 5px;
        }

        .slope-positive { background: #4caf50; color: white; }
        .slope-negative { background: #f44336; color: white; }
        .slope-zero { background: #2196f3; color: white; }
        .slope-undefined { background: #ff9800; color: white; }