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

        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
            line-height: 1.6;
            background: #f5f7fa;
            color: #2c3e50;
            padding: 20px;
            font-size: 15px;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            background: white;
            border-radius: 12px;
            box-shadow: 0 2px 8px rgba(0,0,0,0.1);
            overflow: hidden;
        }

        .header {
            background: linear-gradient(135deg, #2ecc71 0%, #3498db 100%);
            color: white;
            padding: 40px 30px;
            text-align: center;
        }

        .header h1 {
            font-size: 2.2em;
            margin-bottom: 10px;
            font-weight: 600;
            
        }

        .header p {
            font-size: 1.1em;
            opacity: 0.95;
            font-weight: 400;
        }

        .content {
            padding: 30px;
        }

        /* بخش اصلی */
        .main-section {
            margin-bottom: 20px;
            border: 1px solid #e1e8ed;
            border-radius: 8px;
            overflow: hidden;
            background: white;
        }

        .section-header {
            background: #2ecc71;
            color: white;
            padding: 16px 20px;
            cursor: pointer;
            font-weight: 300;
            font-size: 1.1em;
            transition: background 0.3s ease;
            display: flex;
            justify-content: space-between;
            align-items: center;
            user-select: none;
        }

        .section-header:hover {
            background: #27ae60;
        }

        .section-icon {
            font-size: 1.4em;
            transition: transform 0.3s ease;
            font-weight: normal;
        }

        .section-header.collapsed .section-icon {
            transform: rotate(45deg);
        }

        .section-content {
            max-height: 10000px;
            overflow: hidden;
            transition: max-height 0.5s ease;
        }

        .section-content.collapsed {
            max-height: 0;
        }

        .section-body {
            padding: 25px;
            background: #fafafa;
        }

        /* زیربخش‌ها */
        .sub-section {
            margin: 20px 0;
            border: 1px solid #e1e8ed;
            border-radius: 8px;
            overflow: hidden;
            background: white;
        }

        .sub-header {
            background: #90acf8ff;
            color: white;
            padding: 14px 18px;
            cursor: pointer;
            font-weight: 200;
            font-size: 1em;
            transition: background 0.3s ease;
            display: flex;
            justify-content: space-between;
            align-items: center;
            user-select: none;
        }

        .sub-header:hover {
            background: #7698f5ff;
        }

        .sub-icon {
            font-size: 1.3em;
            transition: transform 0.3s ease;
        }

        .sub-header.collapsed .sub-icon {
            transform: rotate(45deg);
        }

        .sub-content {
            max-height: 10000px;
            overflow: hidden;
            transition: max-height 0.5s ease;
        }

        .sub-content.collapsed {
            max-height: 0;
        }

        .sub-body {
            padding: 20px;
            background: #f8f9fa;
        }

        /* کادرهای تعریف */
        .definition-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
            gap: 20px;
            margin: 25px auto;
            max-width: 100%;
            justify-items: center;
        }

        .definition-card {
            background: white;
            padding: 20px;
            border-radius: 8px;
            border: 2px solid #e1e8ed;
            box-shadow: 0 2px 6px rgba(0,0,0,0.08);
            transition: transform 0.3s ease, box-shadow 0.3s ease;
            text-align: center;
            width: 100%;
        }

        .definition-card:hover {
            transform: translateY(-4px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }

        .definition-card h3 {
            color: #2c3e50;
            margin-bottom: 12px;
            font-size: 1.1em;
            font-weight: 600;
        }

        .definition-card p {
            font-size: 0.95em;
            line-height: 1.7;
            color: #555;
        }

        /* لیست اهمیت */
        .importance-list {
            counter-reset: importance;
            list-style: none;
            padding: 0;
        }

        .importance-list li {
            counter-increment: importance;
            margin: 15px 0;
            padding: 18px 20px;
            background: white;
            border-radius: 8px;
            border-right: 4px solid #2ecc71;
            position: relative;
            padding-left: 60px;
            font-size: 0.95em;
            box-shadow: 0 2px 4px rgba(0,0,0,0.06);
        }

        .importance-list li::before {
            content: counter(importance);
            position: absolute;
            left: 18px;
            top: 50%;
            transform: translateY(-50%);
            background: #2ecc71;
            color: white;
            width: 32px;
            height: 32px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: 600;
        }

        /* مراحل انجام */
        .method-steps {
            background: white;
            padding: 20px;
            border-radius: 8px;
            margin: 20px 0;
            border: 1px solid #e1e8ed;
        }

        .method-steps h4 {
            color: #2c3e50;
            margin-bottom: 15px;
            font-size: 1.05em;
            font-weight: 600;
        }

        .step-timeline {
            padding: 0;
        }

        .timeline-item {
            margin: 12px 0;
            padding: 15px;
            background: #f8f9fa;
            border-radius: 6px;
            border-right: 3px solid #3498db;
            font-size: 0.95em;
        }

        .timeline-item strong {
            color: #2980b9;
        }

        .timeline-item ul {
            margin-top: 10px;
            padding-right: 25px;
        }

        .timeline-item li {
            margin: 6px 0;
        }

        /* فرمول */
        .formula-box {
            background: #2ecc71;
            color: white;
            padding: 20px;
            border-radius: 8px;
            text-align: center;
            font-size: 1em;
            margin: 20px auto;
            max-width: 90%;
            box-shadow: 0 2px 8px rgba(46, 204, 113, 0.3);
        }

        /* تصاویر */
        .image-container {
            text-align: center;
            margin: 30px 0;
            padding: 25px;
            background: white;
            border-radius: 8px;
            border: 1px solid #e1e8ed;
        }

        .image-container img {
            max-width: 100%;
            height: auto;
            border-radius: 6px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.1);
        }

        .image-container p {
            margin-top: 15px;
            font-weight: 600;
            color: #2c3e50;
            font-size: 1em;
        }

        /* جداول */
        .table-container {
            overflow-x: auto;
            margin: 20px auto;
            max-width: 100%;
            display: flex;
            justify-content: center;
        }

        table {
            width: 100%;
            max-width: 950px;
            border-collapse: collapse;
            background: white;
            border-radius: 8px;
            overflow: hidden;
            box-shadow: 0 2px 8px rgba(0,0,0,0.08);
            margin: 0 auto;
        }

        th {
            background: #3498db;
            color: white;
            padding: 14px 12px;
            text-align: center;
            font-weight: 600;
            font-size: 0.95em;
        }

        td {
            padding: 12px;
            text-align: center;
            border-bottom: 1px solid #e1e8ed;
            font-size: 0.9em;
        }

        tr:nth-child(even) {
            background: #f8f9fa;
        }

        tr:hover {
            background: #e8f5e9;
        }

        /* باکس‌های توجه */
        .highlight {
            background: #fff9e6;
            padding: 18px;
            border-radius: 8px;
            border-right: 4px solid #ffc107;
            margin: 20px 0;
            font-size: 0.95em;
            line-height: 1.7;
        }

        .note-box {
            background: #e3f2fd;
            padding: 18px;
            border-radius: 8px;
            border-right: 4px solid #3498db;
            margin: 20px 0;
            font-size: 0.95em;
            line-height: 1.7;
        }

        .warning-box {
            background: #ffebee;
            padding: 18px;
            border-radius: 8px;
            border-right: 4px solid #f44336;
            margin: 20px 0;
            font-size: 0.95em;
            line-height: 1.7;
        }

         /* لینک‌ها */
        a {
            color: #3498db;
            text-decoration: none;
            transition: color 0.3s ease;
        }

        a:hover {
            color: #2980b9;
        }
        
         /* کدهای پیغام */
        .message-code {
            background: #f4f4f4;
            padding: 3px 8px;
            border-radius: 4px;
            font-family: 'Courier New', monospace;
            font-size: 0.9em;
            color: #e74c3c;
        }

        /* خط جداکننده */
        .separator {
            height: 2px;
            background: linear-gradient(90deg, #2ecc71 0%, #3498db 100%);
            margin: 35px 0;
            border-radius: 2px;
        }

        @media (max-width: 768px) {
            body {
                font-size: 14px;
                padding: 10px;
            }

            .header h1 {
                font-size: 1.8em;
            }

            .section-header {
                font-size: 1em;
                padding: 14px 16px;
            }

            .definition-grid {
                grid-template-columns: 1fr;
            }

            .content {
                padding: 20px;
            }
        }