:root {
            --primary: #4361ee;
            --primary-dark: #3a56d4;
            --secondary: #7209b7;
            --dark: #212529;
            --light: #f8f9fa;
            --gray: #6c757d;
            --success: #4cc9f0;
            --warning: #f8961e;
            --danger: #ef233c;
            --border-radius: 12px;
            --shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
            --transition: all 0.3s ease;
        }
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        .main-container {
            background: linear-gradient(135deg, #f5f7fa 0%, #e4e7f1 100%);
            color: var(--dark);
            line-height: 1.6;
            min-height: 100vh;
            padding: 20px;
        }
        
        .container {
            width: 95%;
            margin: 0 auto;
        }
        
        .header-title {
            text-align: center;
            padding: 40px 20px;
        }
        
        h1 {
            font-size: 2.8rem;
            margin-bottom: 15px;
            background: linear-gradient(90deg, var(--primary), var(--secondary));
            -webkit-background-clip: text;
            background-clip: text;
            color: transparent;
            font-weight: 800;
        }
        
        .subtitle {
            font-size: 1.2rem;
            color: var(--gray);
            max-width: 700px;
            margin: 0 auto 30px;
        }
        
        .calculator-container {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 30px;
            margin-bottom: 40px;
        }
        
        @media (max-width: 900px) {
            .calculator-container {
                grid-template-columns: 1fr;
            }
        }
        
        .control-panel {
            background: #fff;
            border-radius: var(--border-radius);
            box-shadow: var(--shadow);
            padding: 30px;
        }
        
        .shape-selector {
            margin-bottom: 25px;
        }
        
        select {
            width: 100%;
            padding: 12px 15px;
            border: 1px solid #dee2e6;
            border-radius: 8px;
            font-size: 1rem;
            transition: var(--transition);
            appearance: none;
            background-image: url("data:image/svg+xml;charset=UTF-8,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='currentColor' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3e%3cpolyline points='6 9 12 15 18 9'%3e%3c/polyline%3e%3c/svg%3e");
            background-repeat: no-repeat;
            background-position: right 10px center;
            background-size: 1em;
        }
        
        select:focus {
            outline: none;
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(67, 97, 238, 0.2);
        }
        
        .input-fields {
            display: grid;
            gap: 15px;
        }
        
        .input-group {
            display: flex;
            flex-direction: column;
        }
        
        label {
            margin-bottom: 8px;
            font-weight: 500;
            color: var(--dark);
        }
        
        input {
            padding: 12px 15px;
            border: 1px solid #dee2e6;
            border-radius: 8px;
            font-size: 1rem;
            transition: var(--transition);
        }
        
        input:focus {
            outline: none;
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(67, 97, 238, 0.2);
        }
        
        button {
            background: var(--primary);
            color: white;
            border: none;
            padding: 12px 20px;
            border-radius: 8px;
            cursor: pointer;
            font-weight: 600;
            transition: var(--transition);
            display: flex;
            align-items: center;
            justify-content: center;
            margin-top: 20px;
            width: 100%;
        }
        
        button:hover {
            background: var(--primary-dark);
            transform: translateY(-2px);
        }
        
        button i {
            margin-right: 8px;
        }
        
        .results-panel {
            background: #fff;
            border-radius: var(--border-radius);
            box-shadow: var(--shadow);
            padding: 30px;
            display: flex;
            flex-direction: column;
        }
        
        .shape-display {
            flex-grow: 1;
            display: flex;
            align-items: center;
            justify-content: center;
            margin-bottom: 30px;
        }
        
        .shape-svg {
            max-width: 100%;
            height: auto;
        }
        
        .result-card {
            background: #f8f9fa;
            border-radius: 10px;
            padding: 20px;
            margin-bottom: 15px;
        }
        
        .result-title {
            display: flex;
            align-items: center;
            margin-bottom: 10px;
            color: var(--primary);
            font-weight: 600;
        }
        
        .result-title i {
            margin-right: 10px;
            font-size: 1.2rem;
        }
        
        .result-value {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--dark);
        }
        
        .formula {
            font-family: 'Courier New', Courier, monospace;
            background: #e9ecef;
            padding: 5px 10px;
            border-radius: 5px;
            font-size: 0.9rem;
            margin-top: 10px;
        }
        
        .unit-selector {
            display: flex;
            gap: 10px;
            margin-top: 10px;
        }
        
        .unit-btn {
            padding: 5px 10px;
            border-radius: 5px;
            background: #878c91;
            border: none;
            cursor: pointer;
            font-size: 0.8rem;
            transition: var(--transition);
        }
        
        .unit-btn.active {
            background: var(--primary);
            color: white;
        }
        
        .history {
            margin-top: 20px;
            padding-top: 20px;
            border-top: 1px dashed #dee2e6;
        }
        
        .history-title {
            display: flex;
            align-items: center;
            margin-bottom: 15px;
            color: var(--gray);
        }
        
        .history-items {
            display: grid;
            gap: 10px;
        }
        
        .history-item {
            background: #f8f9fa;
            padding: 10px 15px;
            border-radius: 8px;
            font-size: 0.9rem;
            display: flex;
            justify-content: space-between;
        }
        
        .history-shape {
            font-weight: 600;
        }
        
        .history-value {
            color: var(--primary);
            font-weight: 600;
        }
        
        .features {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 25px;
            margin: 40px 0;
        }
        
        .feature-card {
            background: white;
            padding: 25px;
            border-radius: var(--border-radius);
            box-shadow: var(--shadow);
            transition: var(--transition);
        }
        
        .feature-card:hover {
            transform: translateY(-5px);
        }
        
        .feature-card i {
            font-size: 2.5rem;
            color: var(--primary);
            margin-bottom: 15px;
        }
        
        .feature-card h3 {
            margin-bottom: 10px;
            color: var(--dark);
        }
        
        
        
        .notification {
            position: fixed;
            top: 20px;
            right: 20px;
            padding: 15px 25px;
            background: #4CAF50;
            color: white;
            border-radius: 8px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.15);
            transform: translateX(150%);
            transition: transform 0.3s ease;
            z-index: 1000;
        }
        
        .notification.show {
            transform: translateX(0);
        }
        
        @media (max-width: 600px) {
            h1 {
                font-size: 2.2rem;
            }
            
            .calculator-container {
                padding: 0 10px;
            }
            
            .control-panel, .results-panel {
                padding: 20px;
            }
        }


 /* ===== ARTICLE SPECIFIC STYLES - NO BODY STYLES ===== */
 #perimeter-guide-article {
      width: 95%;
      margin: 0 auto;
      padding: 2rem 1.5rem 3rem 1.5rem;
      font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    }

    /* Hero Section */
    .perimeter-guide-hero {
      text-align: center;
      margin-bottom: 2.5rem;
      padding: 2rem 1.5rem;
      background: linear-gradient(135deg, #4361ee 0%, #7209b7 100%);
      border-radius: 32px;
      box-shadow: 0 12px 30px rgba(67, 97, 238, 0.3);
    }

    .perimeter-guide-hero h2 {
      font-size: 2.6rem;
      font-weight: 800;
      color: white;
      margin-bottom: 1rem;
      letter-spacing: -0.02em;
      font-family: 'Montserrat', serif;
    }

    .perimeter-guide-hero .perimeter-hero-sub {
      font-size: 1.2rem;
      color: rgba(255, 255, 255, 0.9);
      max-width: 720px;
      margin: 0 auto;
      line-height: 1.5;
    }

    .perimeter-guide-meta {
      display: flex;
      justify-content: center;
      gap: 2rem;
      color: rgba(255, 255, 255, 0.8);
      font-weight: 500;
      margin-top: 1.2rem;
      flex-wrap: wrap;
    }

    .perimeter-guide-meta span i {
      margin-right: 0.5rem;
    }

    /* Main Content */
    .perimeter-main-content {
      background: white;
      border-radius: 28px;
      padding: 2rem 2rem 2.5rem 2rem;
      box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
      border: 1px solid rgba(67, 97, 238, 0.15);
    }

    .perimeter-main-content h2 {
      font-size: 1.8rem;
      font-weight: 700;
      margin-top: 2rem;
      margin-bottom: 1rem;
      color: #4361ee;
      border-left: 5px solid #7209b7;
      padding-left: 1rem;
      font-family: 'Montserrat', serif;
    }

    .perimeter-main-content h2:first-of-type {
      margin-top: 0;
    }

    .perimeter-main-content h3 {
      font-size: 1.35rem;
      font-weight: 600;
      margin: 1.5rem 0 0.75rem 0;
      color: #7209b7;
    }

    .perimeter-main-content p {
      font-size: 1.05rem;
      color: #2d3748;
      margin-bottom: 1.2rem;
      line-height: 1.6;
    }

    .perimeter-main-content ul, .perimeter-main-content ol {
      margin: 1rem 0 1.2rem 1.8rem;
      color: #2d3748;
      line-height: 1.6;
    }

    .perimeter-main-content li {
      margin-bottom: 0.5rem;
    }

    .perimeter-highlight-box {
      background: linear-gradient(135deg, rgba(67, 97, 238, 0.08), rgba(114, 9, 183, 0.05));
      border-left: 6px solid #7209b7;
      padding: 1.25rem 1.5rem;
      border-radius: 20px;
      margin: 1.75rem 0;
    }

    .perimeter-pro-tip {
      background: rgba(114, 9, 183, 0.1);
      border-radius: 20px;
      padding: 1.2rem 1.5rem;
      margin: 1.5rem 0;
      display: flex;
      gap: 1rem;
      align-items: flex-start;
      border: 1px solid rgba(67, 97, 238, 0.3);
    }

    .perimeter-pro-tip i {
      font-size: 1.8rem;
      color: #7209b7;
    }

    .perimeter-stats-grid {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
      gap: 1.2rem;
      margin: 2rem 0;
    }

    .perimeter-stat-card {
      background: #f8f9fa;
      border-radius: 20px;
      padding: 1.2rem;
      text-align: center;
      transition: all 0.2s;
      border: 1px solid rgba(67, 97, 238, 0.2);
    }

    .perimeter-stat-card .stat-number {
      font-size: 2rem;
      font-weight: 800;
      color: #4361ee;
      margin-bottom: 0.25rem;
    }

    .perimeter-quote-block {
      background: #f8f9fa;
      padding: 1.5rem;
      border-radius: 24px;
      text-align: center;
      font-style: italic;
      margin: 1.5rem 0;
      border: 1px solid rgba(67, 97, 238, 0.2);
    }

    .perimeter-quote-block i {
      font-size: 2rem;
      color: #7209b7;
      margin-bottom: 0.5rem;
      display: inline-block;
    }

    .perimeter-table-wrapper {
      overflow-x: auto;
      margin: 1.5rem 0;
    }

    .perimeter-formulas-table {
      width: 100%;
      border-collapse: collapse;
      background: #f8f9fa;
      border-radius: 16px;
      overflow: hidden;
    }

    .perimeter-formulas-table th, .perimeter-formulas-table td {
      padding: 12px 16px;
      text-align: left;
      border-bottom: 1px solid rgba(67, 97, 238, 0.2);
    }

    .perimeter-formulas-table th {
      background: rgba(67, 97, 238, 0.1);
      font-weight: 600;
      color: #4361ee;
    }

    .perimeter-formulas-table tr:hover {
      background: rgba(114, 9, 183, 0.05);
    }

    .perimeter-applications-grid {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
      gap: 1.2rem;
      margin: 1.5rem 0;
    }

    .perimeter-app-card {
      background: #f8f9fa;
      border-radius: 16px;
      padding: 1.2rem;
      border: 1px solid rgba(67, 97, 238, 0.2);
      transition: all 0.2s;
    }

    .perimeter-app-card:hover {
      transform: translateY(-3px);
      box-shadow: 0 8px 20px rgba(67, 97, 238, 0.1);
    }

    .perimeter-app-title {
      font-weight: 700;
      color: #4361ee;
      margin-bottom: 0.5rem;
      font-size: 1.1rem;
      display: flex;
      align-items: center;
      gap: 0.5rem;
    }

    .perimeter-footer-note {
      margin-top: 2.5rem;
      text-align: center;
      font-size: 0.85rem;
      color: #718096;
      border-top: 1px solid #e2e8f0;
      padding-top: 2rem;
    }

    @media (max-width: 768px) {
      .perimeter-guide-hero h2 {
        font-size: 2rem;
      }
      .perimeter-main-content {
        padding: 1.5rem;
      }
      #perimeter-guide-article {
        padding: 1rem;
      }
    }