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

 body {
     background: #f4f7fc;
     font-family: 'Segoe UI', Roboto, 'Helvetica Neue', sans-serif;
     line-height: 1.5;
     color: #1a2c3e;
     padding: 2rem 1rem;
 }

 /* main container */
 .container {
     max-width: 1200px;
     margin: 0 auto;
     background: white;
     border-radius: 32px;
     box-shadow: 0 20px 35px -12px rgba(0, 0, 0, 0.1);
     overflow: hidden;
     transition: all 0.2s ease;
 }

 /* header */
 .hero {
     background: linear-gradient(135deg, #0b2b40 0%, #1a4b6e 100%);
     padding: 2.5rem 2rem;
     color: white;
     text-align: center;
 }

 .hero h1 {
     font-size: 2.5rem;
     font-weight: 700;
     letter-spacing: -0.5px;
     margin-bottom: 0.5rem;
 }

 .hero p {
     font-size: 1.2rem;
     opacity: 0.9;
     max-width: 700px;
     margin: 0.75rem auto 0;
 }

 .badge {
     background: rgba(255, 255, 255, 0.2);
     display: inline-block;
     padding: 0.3rem 1rem;
     border-radius: 40px;
     font-size: 0.8rem;
     font-weight: 500;
     margin-top: 1rem;
     backdrop-filter: blur(2px);
 }

 /* content sections */
 .content {
     padding: 2rem 2rem 2.5rem;
 }

 .section {
     margin-bottom: 2.5rem;
     border-bottom: 1px solid #e4edf2;
     padding-bottom: 1.8rem;
 }

 .section:last-child {
     border-bottom: none;
     margin-bottom: 0;
     padding-bottom: 0;
 }

 h2 {
     font-size: 1.8rem;
     font-weight: 600;
     color: #0f3b4f;
     margin-bottom: 1rem;
     display: flex;
     align-items: center;
     gap: 0.5rem;
 }

 h2::before {
     content: "•";
     color: #2c7da0;
     font-size: 2rem;
     font-weight: bold;
 }

 h3 {
     font-size: 1.3rem;
     font-weight: 600;
     color: #1f5e7e;
     margin: 1.2rem 0 0.6rem 0;
 }

 .grid-cards {
     display: flex;
     flex-wrap: wrap;
     gap: 1.5rem;
     margin: 1.5rem 0 0.5rem;
 }

 .card {
     background: #f9fdfe;
     border-left: 5px solid #2c7da0;
     padding: 1.2rem 1.5rem;
     flex: 1 1 250px;
     border-radius: 20px;
     box-shadow: 0 4px 10px rgba(0, 0, 0, 0.02);
     transition: transform 0.2s, box-shadow 0.2s;
     border: 1px solid #e2edf2;
 }

 .card:hover {
     transform: translateY(-3px);
     box-shadow: 0 12px 20px -12px rgba(0, 0, 0, 0.12);
     background: white;
 }

 .card strong {
     display: block;
     font-size: 1.2rem;
     color: #0f3b4f;
     margin-bottom: 0.5rem;
 }

 .card p {
     color: #2c4b5f;
     font-size: 0.95rem;
 }

 .principle-list {
     display: grid;
     grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
     gap: 1rem;
     margin: 1.2rem 0;
 }

 .principle-item {
     background: #f0f6fa;
     padding: 0.9rem 1rem;
     border-radius: 18px;
     font-weight: 500;
     display: flex;
     align-items: center;
     gap: 0.6rem;
     font-size: 0.95rem;
 }

 .principle-item span:first-child {
     font-weight: 700;
     color: #1f6e93;
     min-width: 40px;
 }

 .highlight {
     background: #e8f0f5;
     padding: 1.2rem 1.5rem;
     border-radius: 24px;
     margin: 1.5rem 0 0.5rem;
     border-left: 4px solid #2c7da0;
 }

 .footer-note {
     background: #eef3f7;
     text-align: center;
     padding: 1.2rem;
     border-radius: 28px;
     margin-top: 2rem;
     font-weight: 500;
     color: #1f5e7e;
 }

 .azop-box {
     display: flex;
     flex-wrap: wrap;
     justify-content: space-between;
     align-items: center;
     background: #eef3f8;
     border-radius: 24px;
     padding: 1.2rem 1.8rem;
     margin-top: 1rem;
 }

 .azop-text {
     flex: 2;
 }

 .small-note {
     font-size: 0.85rem;
     color: #2f6b8c;
     margin-top: 0.3rem;
 }

 hr {
     margin: 1rem 0;
     border: 0;
     height: 1px;
     background: linear-gradient(to right, #cbdbe2, transparent);
 }

 @media (max-width: 700px) {
     .hero h1 {
         font-size: 1.9rem;
     }

     .content {
         padding: 1.5rem;
     }

     h2 {
         font-size: 1.5rem;
     }

     .principle-list {
         grid-template-columns: 1fr;
     }
 }

 button,
 .quiz-block {
     background: none;
 }

 .review-question {
     background: #ffffff;
     border: 1px solid #cde3ec;
     border-radius: 24px;
     padding: 1.2rem 1.5rem;
     margin-top: 1.5rem;
 }

 .review-question p {
     font-weight: 600;
     margin: 0.5rem 0;
 }

 .question-item {
     margin: 1rem 0 0.5rem;
     border-left: 3px solid #2c7da0;
     padding-left: 1rem;
 }

 .answer-line {
     color: #1a5d7a;
     font-style: italic;
 }