:root{--font-serif: 'Source Serif 4', Georgia, serif;--font-sans: 'Source Sans 3', -apple-system, BlinkMacSystemFont, sans-serif;--color-text: #2c3e50;--color-text-light: #5a6c7d;--color-heading: #1a252f;--color-link: #2874a6;--color-link-hover: #1a4f72;--color-bg: #ffffff;--color-bg-alt: #f8f9fa;--color-border: #e9ecef;--color-border-light: #f0f2f4;--color-accent: #27ae60;--color-navy: #1a3a5c;--color-navy-dark: #0f2840;--color-navy-light: #e8f0f8;--max-width: 1200px;--content-width: 720px;--spacing: 1.5rem}*,*::before,*::after{box-sizing:border-box}html{font-size:18px;scroll-behavior:smooth}body{margin:0;font-family:var(--font-serif);font-size:1rem;line-height:1.7;color:var(--color-text);background:var(--color-bg)}h1,h2,h3,h4,h5,h6{font-family:var(--font-serif);font-weight:600;color:var(--color-heading);line-height:1.3;margin-top:1.5rem;margin-bottom:0.75rem}h1{font-size:2.25rem}h2{font-size:1.75rem}h3{font-size:1.35rem}h4{font-size:1.15rem}p{margin:0 0 1rem}a{color:var(--color-link);text-decoration:none;transition:color 0.2s ease}a:hover{color:var(--color-link-hover);text-decoration:underline}.site-header{border-bottom:1px solid var(--color-border-light);padding:0.75rem 0;background:var(--color-bg);position:sticky;top:0;z-index:100}.site-nav{max-width:var(--max-width);margin:0 auto;padding:0 var(--spacing);display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:0.75rem}.site-title{font-family:var(--font-serif);font-size:1.25rem;font-weight:600;color:var(--color-heading);text-decoration:none}.site-title:hover{color:var(--color-link);text-decoration:none}.nav-links{list-style:none;margin:0;padding:0;display:flex;gap:1.5rem;flex-wrap:wrap}.nav-links li{margin:0}.nav-links a{font-family:var(--font-sans);font-size:0.9rem;color:var(--color-text-light);text-decoration:none;padding:0.2rem 0;border-bottom:2px solid transparent;transition:all 0.2s ease}.nav-links a:hover,.nav-links 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p{color:var(--color-text-light);font-size:0.9rem;margin-bottom:0.75rem}.landing-about p:last-child{margin-bottom:0}.site-footer{border-top:1px solid var(--color-border-light);background:var(--color-bg-alt);padding:1.5rem 0}.footer-content{max-width:var(--max-width);margin:0 auto;padding:0 var(--spacing);text-align:center;font-family:var(--font-sans);font-size:0.8rem;color:var(--color-text-light)}.footer-content p{margin:0.2rem 0}.footer-content a{color:var(--color-text-light)}.footer-content a:hover{color:var(--color-link)}.page-content{max-width:var(--content-width);margin:0 auto;padding:2rem var(--spacing)}.page-header{margin-bottom:1.5rem}.page-header h1{margin:0 0 0.5rem}.subtitle{font-size:1.1rem;color:var(--color-text-light);margin:0}.page-container{max-width:var(--content-width);margin:1.5rem auto;padding:1.5rem 2rem;background:var(--color-bg);border:1px solid var(--color-border-light);border-radius:4px}.blog-index{max-width:var(--content-width);margin:0 auto;padding:2rem var(--spacing)}.blog-header{margin-bottom:2rem}.blog-header h1{margin-bottom:0.5rem}.blog-header .description{color:var(--color-text-light);font-size:1.05rem}.post-list{list-style:none;padding:0;margin:0}.post-list li{padding:1.25rem 0;border-bottom:1px solid var(--color-border-light)}.post-list li:first-child{padding-top:0}.post-list h2{font-size:1.25rem;margin:0 0 0.4rem}.post-list h2 a{color:var(--color-heading)}.post-list .post-meta{font-family:var(--font-sans);font-size:0.8rem;color:var(--color-text-light);margin-bottom:0.4rem}.post-list .excerpt{margin:0;color:var(--color-text-light);font-size:0.95rem}.blog-post{max-width:var(--content-width);margin:0 auto;padding:2rem var(--spacing)}.post-header{margin-bottom:2rem}.post-header h1{margin:0 0 0.5rem}.post-header .post-meta{font-family:var(--font-sans);font-size:0.85rem;color:var(--color-text-light)}.post-content{margin-bottom:2rem}.post-footer{padding-top:1.5rem;border-top:1px solid var(--color-border-light)}.post-footer a{font-family:var(--font-sans);font-size:0.85rem}.course-site{min-height:100vh;display:flex;flex-direction:column}.course-banner{background:url("/course/images/NASA_earth_at_night.jpg") center/cover no-repeat;background-color:#0a1628;text-align:center}.course-banner-inner{max-width:var(--max-width);margin:0 auto;color:#fff;text-shadow:0 2px 10px rgba(0,0,0,0.8)}.course-banner h1{margin:0 0 0.25rem 0;color:#fff;font-weight:600}.course-banner p{margin:0;font-family:var(--font-sans);opacity:0.9}.course-banner-large{padding:5rem 1.5rem}.course-banner-large h1{font-size:2.75rem}.course-banner-large p{font-size:1.25rem}.course-banner-small{padding:1.25rem 1.5rem}.course-banner-small .course-banner-inner{text-align:left}.banner-home-link{font-family:var(--font-serif);font-size:1.15rem;font-weight:500;color:#fff;text-decoration:none;text-shadow:0 1px 4px rgba(0,0,0,0.5)}.banner-home-link:hover{color:#fff;text-decoration:underline}.course-banner-home{background-size:100% auto;background-position:center center;background-repeat:no-repeat;padding:6.5rem 1.5rem}.course-banner-home h1{font-size:2.75rem}.course-banner-home p{font-size:1.25rem}.course-home-content{max-width:900px;margin:0 auto;padding:2.5rem 1.5rem}.challenges-list{margin:1rem 0 1rem 1.5rem}.challenges-list p{margin-bottom:0.75rem}.challenges-list p:last-child{margin-bottom:0}.part-card{background:#ffffff;border:1px solid #d0dce8;border-radius:6px;margin-bottom:1rem;overflow:hidden}.part-card-header{background:var(--color-navy);padding:0.75rem 1.25rem}.part-card-header a{color:white;text-decoration:none;font-weight:600;font-size:1.1rem}.part-card-header a:hover{text-decoration:underline}.part-card-units{padding:1rem 1.25rem}.part-card-units ul{list-style:none;margin:0;padding:0;columns:2;column-gap:2rem}.part-card-units li{padding:0.25rem 0;break-inside:avoid}.part-card-units a{color:var(--color-navy);text-decoration:none;font-size:0.95rem}.part-card-units a:hover{text-decoration:underline;color:var(--color-navy-dark)}.library-section{margin-top:2.5rem;padding-top:2rem;border-top:1px solid #e0e0e0}.library-heading{font-size:1.25rem;font-weight:600;color:var(--color-navy);margin-bottom:1rem}.library-links{display:flex;flex-wrap:wrap;gap:0.5rem 1.5rem}.library-links a{color:var(--color-navy);text-decoration:none;font-size:0.95rem;padding:0.4rem 0}.library-links a:hover{text-decoration:underline}.c4sd-banner{width:100%;display:flex;justify-content:center;align-items:center;background:#f5f0e8;padding:2rem 1rem}.c4sd-banner img{max-width:1000px;width:100%;height:auto;display:block}.page-container-tight{max-width:800px;margin:0 auto;padding:2rem 1.5rem}.page-container-tight .page-title{font-size:2rem;margin-bottom:0.5rem}.page-container-tight .page-subtitle{margin-top:0;margin-bottom:1.5rem;color:#4a5568}.about-links{display:flex;justify-content:center;gap:1.5rem;margin-top:2rem}.about-link{color:var(--color-navy);text-decoration:none;font-weight:600;font-size:1.05rem;padding:0.5rem 0;border-bottom:2px solid var(--color-navy)}.about-link:hover{color:var(--color-navy-dark);border-bottom-color:var(--color-navy-dark)}.pdf-download-btn{display:inline-block;padding:10px 20px;background:var(--color-navy);color:white;border-radius:4px;text-decoration:none;font-weight:500;font-size:0.95rem;margin-top:1.5rem}.pdf-download-btn:hover{background:var(--color-navy-dark);color:white}.course-layout{display:flex;max-width:1100px;margin:0 auto;padding:1.5rem 1.5rem 1.5rem 0.5rem;gap:0;flex:1;background:#ffffff}.course-content{flex:1;min-width:0;max-width:780px;padding:1.5rem 2rem;margin-left:8px;background:#ffffff}.course-content h1:first-child{margin-top:0}.course-sidebar{width:250px;flex-shrink:0;background:#ffffff;border-right:1px solid #d0dce8;padding:15px}.sidebar-divider{height:1px;background:#d0dce8;margin:15px 0}.sidebar-section-group{margin-bottom:0}.sidebar-part{margin-bottom:2px}.sidebar-part-header{display:flex;align-items:center;padding:10px 5px;cursor:pointer;border-bottom:1px solid #e8e8e8;transition:background 0.15s ease}.sidebar-part-header:hover{background:var(--color-navy-light)}.sidebar-arrow{margin-right:8px;font-size:0.7rem;color:var(--color-navy);width:12px;flex-shrink:0}.sidebar-part-title{font-family:var(--font-sans);font-size:0.9rem;font-weight:600;color:var(--color-navy)}.sidebar-units{list-style:none;padding:0;margin:0;display:none;background:#ffffff}.sidebar-units.expanded{display:block}.sidebar-units li{padding:0;border-bottom:1px solid #f0f0f0}.sidebar-units li:last-child{border-bottom:none}.sidebar-units a{display:block;font-family:var(--font-sans);font-size:0.85rem;color:var(--color-navy);padding:8px 8px 8px 24px;text-decoration:none;transition:background 0.15s ease}.sidebar-units a:hover{background:var(--color-navy-light);text-decoration:none}.sidebar-units a.active{font-weight:600;color:var(--color-navy-dark);background:var(--color-navy-light)}.course-unit-footer{margin-top:2rem;padding-top:1rem;border-top:1px solid var(--color-border-light);font-family:var(--font-sans);font-size:0.8rem;color:var(--color-text-light)}.course-unit-footer a{color:var(--color-text-light)}.course-unit-footer p{margin:0}.course-home-container{max-width:var(--content-width);margin:0 auto;padding:2rem var(--spacing);flex:1}.course-home-container h1:first-child{margin-top:0}.course-footer-full{border-top:1px solid var(--color-border-light);background:var(--color-bg-alt);padding:2rem var(--spacing);margin-top:auto}.course-footer-inner{max-width:var(--content-width);margin:0 auto;font-family:var(--font-sans);font-size:0.85rem;color:var(--color-text-light)}.course-footer-inner p{margin:0.4rem 0}.course-footer-inner a{color:var(--color-link)}.footer-free{margin-bottom:1rem !important}.footer-copyright{font-weight:600;color:var(--color-text)}.footer-contact{margin-top:1rem !important}.footer-links{margin-top:1rem !important;padding-top:1rem;border-top:1px solid var(--color-border-light)}.footer-sep{margin:0 0.75rem;color:var(--color-border)}.section-grid{display:flex;flex-direction:column;gap:1rem;margin-top:1.5rem}.section-card{padding:1.25rem;background:var(--color-bg-alt);border:1px solid var(--color-border-light);border-radius:4px;transition:border-color 0.2s, box-shadow 0.2s}.section-card:hover{border-color:#d0d7de;box-shadow:0 2px 6px rgba(0,0,0,0.04)}.section-card h3{font-size:1.15rem;margin-top:0;margin-bottom:0.5rem;border-bottom:none;padding-bottom:0}.section-card p{font-size:0.95rem;color:var(--color-text-light);margin-bottom:0;line-height:1.5}.section-card a.card-link{display:block;margin-top:0.75rem;font-family:var(--font-sans);font-size:0.9rem;font-weight:500}.section-card.card-course{background:#e8f4f8;border-color:#d4e5ec}.section-card.card-blog{background:#fef9e7;border-color:#ede4c8}.section-card.card-keeping{background:#f0f7f0;border-color:#d4e5d4}.section-card.card-c4sd{background:#f5f0fa;border-color:#e0d4eb}.section-card.card-sub{padding:1rem 1.25rem}.section-card.card-sub h3{font-size:1rem}table{width:100%;border-collapse:collapse;margin:1.25rem 0;font-size:0.9rem}th,td{padding:0.6rem 0.8rem;text-align:left;border:1px solid var(--color-border-light)}th{background:var(--color-bg-alt);font-family:var(--font-sans);font-weight:600}.text-center{text-align:center}.text-small{font-size:0.9rem}.text-muted{color:var(--color-text-light)}.mt-0{margin-top:0}.mb-0{margin-bottom:0}.figure-caption{font-size:0.8rem;font-style:italic;color:var(--color-text-light);text-align:center;margin-top:-0.75rem;margin-bottom:1.25rem}img{max-width:100%;height:auto;display:block;margin:1.25rem auto}blockquote{margin:1.25rem 0;padding:0.75rem 1.25rem;border-left:3px solid #d0d7de;background:var(--color-bg-alt);color:var(--color-text-light);font-style:italic}blockquote p:last-child{margin-bottom:0}hr{border:none;border-top:1px solid var(--color-border-light);margin:1.5rem 0}ul,ol{margin:0 0 1rem 0;padding-left:1.25rem}li{margin-bottom:0.3rem}sup{font-size:0.75em;line-height:0}@media (max-width: 900px){.course-layout{flex-direction:column;gap:0}.course-sidebar{width:100%;order:-1;border-right:none;border-bottom:1px solid #d0dce8}.course-content{margin-left:0;border:none;border-top:1px solid #d0dce8}}@media (max-width: 800px){.page-container{margin:1rem;padding:1rem 1.25rem}}@media (max-width: 600px){html{font-size:16px}.site-nav{flex-direction:column;align-items:flex-start}.nav-links{gap:1rem}.landing-hero h1{font-size:2rem}.landing-hero{padding:3rem var(--spacing)}.section-card-full{flex-direction:column}.section-card-full .card-image{width:100%;min-height:100px}.course-banner-large{padding:3rem 1rem}.course-banner-large h1{font-size:2rem}.course-banner-home{padding:4.5rem 1rem}.course-banner-home h1{font-size:2rem}.part-card-units ul{columns:1}.library-links{flex-direction:column;gap:0.5rem}.about-links{flex-direction:column;gap:0.75rem}.course-layout{padding:1rem}.course-content{padding:1rem}}@media print{.site-header,.site-footer,.course-nav-bar,.course-sidebar{display:none}.course-layout{display:block}.course-content{border:none;margin:0;padding:0}.page-container{border:none;margin:0;padding:0}}.earth-banner{background:url("/course/images/NASA_earth_at_night.jpg") center/cover no-repeat;background-color:#0a1628;text-align:center}.earth-banner-small{padding:4rem 1.5rem}.earth-banner-inner{max-width:var(--max-width);margin:0 auto;color:#fff;text-shadow:0 2px 10px rgba(0,0,0,0.8)}.earth-banner-inner h1{margin:0;color:#fff;font-weight:600;font-size:2rem}.custom-banner{text-align:center;min-height:180px;display:flex;align-items:center;justify-content:center;background-color:#1a1a1a}.custom-banner .earth-banner-inner{max-width:var(--max-width);margin:0 auto;padding:2rem 1.5rem}.custom-banner .earth-banner-inner h1{margin:0;color:#fff;font-weight:600;font-size:2rem;text-shadow:0 2px 10px rgba(0,0,0,0.8)}