:root{--navy:#0c1b34;--deep:#071627;--ink:#172a42;--muted:#50637b;--teal:#087f82;--teal2:#11a7a3;--mint:#e0faf1;--purple:#7956d6;--lavender:#f0eafe;--sky:#e6f4ff;--sun:#ffdd83;--paper:#f5f8fc;--white:#fff;--line:#dbe5ee;--radius:20px;--shadow:0 15px 45px rgba(19,40,69,.07)}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--paper);font:400 17px/1.65 system-ui,-apple-system,"Segoe UI",Arial,sans-serif;color:var(--ink)}a{color:#075f75}a:hover{text-decoration-thickness:2px}button,input,select{font:inherit}button{cursor:pointer}button:disabled{opacity:.55;cursor:not-allowed}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible,summary:focus-visible{outline:3px solid #db8b29;outline-offset:3px}h1,h2,h3,p{margin-top:0}h1,h2,h3{line-height:1.19;letter-spacing:-.025em;color:var(--navy)}h1{font-size:clamp(2.55rem,5vw,4.65rem)}h2{font-size:clamp(1.75rem,3vw,2.6rem)}h3{font-size:1.26rem}p{max-width:75ch}img,svg{max-width:100%}.sr-only{position:absolute!important;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap} .skip{position:absolute;left:1rem;top:-100px;z-index:1000;background:#fff;padding:12px;border-radius:8px}.skip:focus{top:10px}.wrap{width:min(1200px,calc(100% - 44px));margin-inline:auto}
.site-header{background:#fff;position:sticky;top:0;z-index:100;border-bottom:1px solid #e1e8f0;box-shadow:0 4px 20px rgba(3,27,47,.04)}.header-inner{display:flex;align-items:center;justify-content:space-between;gap:16px;min-height:84px}.brand{display:flex;align-items:center;gap:10px;text-decoration:none;min-width:223px}.brand-mark{width:47px;height:47px;flex-shrink:0}.brand-word{font-size:1.1rem;font-weight:850;line-height:1.06;color:var(--navy);letter-spacing:-.035em}.brand-word strong{color:var(--teal)}.brand-caption{display:block;font-size:.7rem;font-weight:650;letter-spacing:.04em;color:var(--muted);margin-top:4px}.nav{display:flex;align-items:center;gap:4px}.nav a{display:inline-flex;padding:10px 12px;align-items:center;border-radius:12px;text-decoration:none;font-size:.88rem;white-space:nowrap;font-weight:720;color:#29425b}.nav a:hover,.nav a[aria-current=page]{background:#e5f6f3;color:#006765}.menu-toggle{display:none;align-items:center;justify-content:center;min-height:44px;border:1px solid var(--line);background:#fff;border-radius:12px;padding:8px 14px;font-weight:700;color:var(--navy)}
.hero{background:radial-gradient(ellipse at 73% 18%,#143e60 0,transparent 43%),linear-gradient(120deg,#0a203e,#0a3047 72%,#0b4d51);overflow:hidden;color:#fff;position:relative}.hero .wrap{display:grid;grid-template-columns:1.05fr .95fr;align-items:center;min-height:590px;gap:32px;padding-block:60px}.hero h1{color:#fff;margin:18px 0 20px}.hero h1 em{font-style:normal;color:#9df1c9}.hero p{font-size:1.16rem;color:#dbeaf3;max-width:600px}.eyebrow{font-weight:850;font-size:.74rem;letter-spacing:.14em;text-transform:uppercase;color:#1b8385}.hero .eyebrow{color:#9df1c9}.hero-actions{display:flex;flex-wrap:wrap;gap:12px;margin:28px 0}.button{display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:49px;padding:12px 21px;border-radius:13px;text-decoration:none;font-weight:790;font-size:.94rem;border:2px solid transparent;line-height:1.35}.button-primary{background:#92e5bc;color:#073c34}.button-primary:hover{background:#b4f9d6}.button-outline{border-color:#ffffffb0;color:#fff;background:transparent}.button-outline:hover{background:#ffffff20}.button-teal{background:var(--teal);color:#fff}.button-teal:hover{background:#09666b}.button-ghost{background:#fff;color:var(--teal);border-color:#cde3e9}.pills{display:flex;gap:9px;flex-wrap:wrap}.pill{display:inline-flex;border-radius:100px;background:#ffffff15;border:1px solid #ffffff3e;padding:7px 12px;font-size:.76rem;font-weight:800;color:#e0f7f4}.hero-orbits{position:relative;min-height:480px;display:flex;align-items:center;justify-content:center}.hero-orbits svg{width:min(100%,570px);filter:drop-shadow(0 12px 25px #00192b55)}.orbit-tag{position:absolute;padding:11px 15px;border:1px solid #abdcef80;border-radius:13px;color:#fff;font-weight:800;font-size:.86rem;backdrop-filter:blur(12px);background:#1f4f67ac}.tag-1{top:15%;left:2%}.tag-2{right:4%;top:21%}.tag-3{bottom:13%;right:5%}.hero-note{position:absolute;bottom:24px;left:20px;color:#bed5e4;font-size:.73rem}
.stats{display:grid;grid-template-columns:repeat(4,1fr);gap:14px;margin-top:-36px;position:relative;z-index:2}.stat{padding:22px 25px;background:#fff;border:1px solid #e6eaf0;border-radius:18px;box-shadow:var(--shadow)}.stat strong{display:block;font-size:2rem;line-height:1.12;color:var(--teal)}.stat span{color:var(--muted);font-weight:700;font-size:.84rem}.section{padding-block:74px}.section-sm{padding-block:48px}.heading-row{display:flex;align-items:end;justify-content:space-between;gap:20px;margin-bottom:26px}.heading-row h2{margin:6px 0 0}.section-intro{color:var(--muted);font-size:1.04rem}.card-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:20px}.card{border-radius:var(--radius);background:#fff;border:1px solid var(--line);overflow:hidden;box-shadow:var(--shadow)}.card-body{padding:24px}.card h3{margin:12px 0 11px}.card p{color:var(--muted);font-size:.94rem}.card a.action{font-size:.93rem;font-weight:820;text-decoration:none;color:#006b70}.card a.action:hover{text-decoration:underline}.card-art{height:166px;display:grid;place-items:center;position:relative;overflow:hidden}.card-art svg{height:140px;width:auto;filter:drop-shadow(0 10px 18px #1c355025)}.art-elements{background:linear-gradient(120deg,#e1f3ff,#d5f1f4)}.art-labs{background:linear-gradient(120deg,#e1f9eb,#d2ebf7)}.art-molecules{background:linear-gradient(120deg,#f1eafa,#dbedfe)}.art-learn{background:linear-gradient(120deg,#fff5d7,#e2efff)}.art-quiz{background:linear-gradient(120deg,#e5f8f2,#f3ebff)}.art-safety{background:linear-gradient(120deg,#e8f0ff,#e6f9ef)}.teaser{background:#edf6f7;border-radius:24px;padding:32px;display:grid;grid-template-columns:1fr 1fr;gap:26px;align-items:center}.teaser p{color:#40596d}.teaser-figure{background:#fff;min-height:290px;border:1px solid #dbebeb;border-radius:20px;display:grid;place-items:center;padding:10px}.ribbon{background:#09253b;color:#fff;padding:27px 0}.ribbon-inner{display:flex;align-items:center;justify-content:space-between;gap:20px}.ribbon h2{font-size:1.6rem;color:#fff;margin:0}.ribbon p{color:#d1e1e9;margin:6px 0 0}.site-footer{background:#081d30;color:#dce9f1;padding:55px 0 23px}.footer-grid{display:grid;grid-template-columns:1.5fr 1fr 1fr;gap:32px}.site-footer a{color:#cee8f2}.site-footer h3{color:#fff;font-size:1rem}.footer-links{display:grid;gap:8px}.footer-bottom{border-top:1px solid #436079;margin-top:36px;padding-top:19px;color:#aec4d4;font-size:.78rem}.site-footer p{font-size:.88rem;color:#b6ccdb}
.page-hero{background:linear-gradient(110deg,#0a2039,#104a53);color:#fff;padding:72px 0 67px}.page-hero h1{color:#fff;font-size:clamp(2.5rem,4.5vw,4.1rem);margin:9px 0 13px}.page-hero p{color:#d5e8ee;font-size:1.1rem;margin-bottom:0}.page-hero .eyebrow{color:#9fe7c6}.content-layout{display:grid;grid-template-columns:minmax(0,1fr) 310px;gap:26px;align-items:start}.panel{background:#fff;border:1px solid var(--line);border-radius:20px;padding:25px;box-shadow:var(--shadow)}.panel h2{font-size:1.42rem}.panel h3{font-size:1.15rem}.micro{font-size:.84rem;color:var(--muted)}.note{padding:16px 19px;border-radius:14px;background:#e7f5fc;border-left:4px solid #1583aa;color:#183f54;font-size:.9rem}.note.warning{background:#fff7df;border-color:#b88324;color:#62491c}.form-row{display:flex;gap:12px;flex-wrap:wrap;align-items:center;margin:16px 0}.form-row label{font-weight:780}.field{min-height:49px;border:1.5px solid #b6c8d6;border-radius:12px;padding:10px 13px;width:100%;background:#fff;color:var(--ink)}.field:focus-visible{outline:3px solid #ffda89;outline-offset:2px}.search-field{max-width:430px}.control{margin:18px 0}.control label{display:block;font-size:.93rem;font-weight:780;margin:0 0 7px}.control input[type=range]{width:100%;accent-color:var(--teal);height:35px}.control .value{font-weight:830;color:var(--teal);font-size:1.08rem}.result{background:#eaf9f2;border:1px solid #bee4d6;border-radius:14px;padding:20px;margin-top:20px}.result strong{font-size:1.2rem;color:#095e4b}.result p{margin-bottom:0;font-size:.9rem}.data-line{display:flex;justify-content:space-between;gap:15px;border-bottom:1px solid var(--line);padding:9px 0}.data-line:last-child{border:0}.data-line b{color:var(--navy)}
.periodic-scroll{overflow-x:auto;max-width:100%;padding:12px 0 18px}.periodic{display:grid;grid-template-columns:repeat(18,minmax(45px,1fr));gap:4px;min-width:940px}.element{border:1px solid #fff8;border-radius:7px;min-height:59px;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:5px 2px;color:#102636;transition:transform .13s ease,box-shadow .13s;position:relative}.element:hover,.element:focus-visible{transform:scale(1.08);z-index:3;box-shadow:0 3px 10px #17304840}.element .el-no{font-size:.62rem;align-self:flex-start;margin-left:4px;line-height:1}.element .el-symbol{font-size:1.14rem;font-weight:900;line-height:1.1}.element .el-name{font-size:.52rem;line-height:1.1;font-weight:650;max-width:100%;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.element.dimmed{opacity:.21}.placeholder{border-radius:7px;background:#eff1f8;color:#506172;font-size:.58rem;font-weight:800;min-height:59px}.periodic-break{grid-column:1/-1;height:16px}.cat-nonmetal{background:#aee8c5}.cat-noble{background:#c6bff9}.cat-alkali{background:#ffc7a5}.cat-alkaline{background:#ffe9ac}.cat-metalloid{background:#bee4e8}.cat-halogen{background:#f5c1da}.cat-transition{background:#c6ddff}.cat-post{background:#d7e5e9}.cat-lanthanide{background:#ffe0ca}.cat-actinide{background:#f9d1f2}.legend{display:flex;flex-wrap:wrap;gap:7px;margin-top:16px}.legend button{border:1px solid #b4c6ce;padding:7px 10px;border-radius:100px;background:#fff;font-size:.74rem;font-weight:780}.legend .swatch{display:inline-block;width:11px;height:11px;border-radius:3px;margin-right:5px}.legend button[aria-pressed=true]{outline:3px solid #67bdb7;outline-offset:1px}.selected-element{position:sticky;top:105px}.big-symbol{border-radius:18px;background:#d6f5e5;padding:20px;width:150px;text-align:center;margin-bottom:17px}.big-symbol span{font-weight:900;font-size:3.3rem;line-height:1;display:block}.big-symbol small{font-size:.85rem;font-weight:750}.element-status{color:#678;min-height:26px;margin-bottom:10px}
.lab-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:17px;margin:32px 0}.lab-tab{border:2px solid #d8e5ef;background:#fff;border-radius:17px;padding:18px;text-align:left;color:var(--ink);min-height:110px}.lab-tab strong{display:block;font-size:1.06rem}.lab-tab span{display:block;color:var(--muted);font-size:.83rem;margin-top:5px}.lab-tab[aria-selected=true]{border-color:#0c8989;background:#e8f7f3}.lab-panel{display:none}.lab-panel.active{display:block}.lab-two{display:grid;grid-template-columns:1fr 1fr;gap:25px;align-items:stretch}.lab-visual{background:linear-gradient(145deg,#edf8fb,#eaf3fb);border:1px solid #dceef0;border-radius:20px;min-height:325px;padding:22px;display:flex;align-items:center;justify-content:center;flex-direction:column}.ph-vessel{width:160px;height:190px;position:relative;border:7px solid #456577;border-top:0;border-radius:0 0 28px 28px;overflow:hidden;background:#fff9;margin:25px auto 14px}.ph-liquid{position:absolute;inset:35% 0 0;background:#58aa4c;transition:background .2s}.ph-vessel:before,.ph-vessel:after{content:"";position:absolute;top:8px;border-radius:12px;height:8px;width:62px;background:#456577;z-index:1}.ph-vessel:before{left:-10px}.ph-vessel:after{right:-10px}.ph-scale{display:grid;grid-template-columns:repeat(15,1fr);gap:2px;width:min(100%,340px);margin:7px auto}.ph-scale i{height:22px;border-radius:3px}.density-vessel{height:225px;width:245px;border:5px solid #42637c;border-top:0;border-radius:0 0 20px 20px;position:relative;margin:10px auto;background:linear-gradient(to top,#83cce0 75%,#fff 75%)}.density-object{width:66px;height:66px;position:absolute;left:calc(50% - 33px);border:3px solid #da8d35;border-radius:17px;background:linear-gradient(140deg,#f9d48d,#deaa68);transition:top .25s ease}.density-object.float{top:15%}.density-object.sink{top:calc(100% - 72px)}.density-object.equal{top:49%}.density-waterline{position:absolute;top:25%;left:0;right:0;border-top:2px dashed #08617e}.atom-svg{width:min(100%,350px);height:auto;min-height:290px}.molecule-list{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin-bottom:24px}.molecule-list button{border:2px solid #d4e3ed;background:#fff;border-radius:15px;padding:16px 8px;font-weight:800;color:var(--navy)}.molecule-list button[aria-pressed=true]{background:#e7f8f3;border-color:#07807b}.molecule-figure{min-height:370px;background:radial-gradient(ellipse,#e0effd,#f7fbff);border:1px solid var(--line);border-radius:20px;display:flex;align-items:center;justify-content:center;padding:25px}.molecule-figure svg{width:min(100%,480px);max-height:350px}.question{font-size:1.27rem;font-weight:800;line-height:1.4;color:var(--navy)}.choice{display:block;width:100%;text-align:left;background:#fff;border:2px solid #d7e3ec;border-radius:14px;padding:15px 17px;font-weight:680;min-height:53px;margin:11px 0}.choice:hover:not(:disabled){background:#eaf7f5}.choice.correct{border-color:#299974;background:#e4f9ed}.choice.incorrect{border-color:#d96465;background:#fff0ed}.quiz-track{height:13px;background:#e7edf2;border-radius:10px;overflow:hidden}.quiz-fill{height:100%;background:var(--teal);transition:width .2s}.quiz-feedback{background:#eaf7f3;border-left:4px solid var(--teal);border-radius:10px;padding:14px 18px;margin:19px 0}.lesson-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:18px}.lesson-card{background:#fff;border:1px solid var(--line);padding:25px;border-radius:18px;box-shadow:var(--shadow)}.lesson-card .lesson-no{display:inline-flex;background:#e3f7f1;border-radius:9px;padding:4px 9px;color:#006e69;font-weight:800;font-size:.8rem}.lesson-card ul{padding-left:22px}.lesson-card li{margin:8px 0}.references{display:grid;gap:12px}.references a{overflow-wrap:anywhere}.prose{background:#fff;border-radius:20px;padding:32px;border:1px solid var(--line)}.prose h2{font-size:1.55rem;margin-top:25px}.prose li{margin-bottom:10px}
@media (max-width:1050px){.nav a{padding:9px 7px;font-size:.78rem}.brand{min-width:205px}.header-inner{gap:5px}.hero .wrap{min-height:540px}.hero-orbits{min-height:380px}}
@media (max-width:830px){.header-inner{min-height:76px}.menu-toggle{display:inline-flex}.nav{display:none;position:absolute;top:76px;left:0;right:0;background:#fff;box-shadow:0 22px 28px #142e5124;flex-direction:column;align-items:stretch;padding:12px 22px 20px}.nav.open{display:flex}.nav a{font-size:1rem;padding:13px 15px}.hero .wrap{grid-template-columns:1fr;gap:10px;padding-top:46px}.hero-orbits{min-height:330px}.hero-orbits svg{max-height:340px}.stats{grid-template-columns:repeat(2,1fr)}.card-grid{grid-template-columns:repeat(2,1fr)}.content-layout,.teaser,.lab-two{grid-template-columns:1fr}.selected-element{position:static}.footer-grid{grid-template-columns:1fr 1fr}.lab-grid{grid-template-columns:1fr 1fr}.molecule-list{grid-template-columns:repeat(2,1fr)}}
@media (max-width:560px){.wrap{width:min(100% - 30px,1200px)}body{font-size:16px}.hero .wrap{padding-block:44px 30px}.hero h1{font-size:clamp(2.4rem,12vw,3.25rem)}.hero p{font-size:1.03rem}.hero-orbits{min-height:290px}.hero-orbits svg{max-height:280px}.orbit-tag{font-size:.65rem;padding:7px 9px}.tag-1{top:8%}.tag-2{top:13%}.tag-3{bottom:7%}.stats{gap:9px;margin-top:12px}.stat{padding:17px}.stat strong{font-size:1.6rem}.stat span{font-size:.74rem}.section{padding-block:45px}.section-sm{padding-block:30px}.card-grid,.lesson-grid,.footer-grid,.lab-grid{grid-template-columns:1fr}.heading-row{align-items:start;flex-direction:column;gap:5px}.card-art{height:150px}.page-hero{padding:50px 0}.panel{padding:17px}.teaser{padding:20px}.ribbon-inner{align-items:start;flex-direction:column}.brand-word{font-size:1.01rem}.brand-mark{width:42px;height:42px}.big-symbol{width:130px}.form-row{align-items:stretch;flex-direction:column}.form-row>*{width:100%}.lab-visual{min-height:280px}.molecule-figure{min-height:260px}.prose{padding:20px}}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{transition:none!important;animation:none!important}}
@media print{.site-header,.site-footer,.menu-toggle,.button{display:none!important}body{background:#fff;color:#111}.wrap{width:100%}.page-hero{background:#fff;padding:16px 0;color:#111}.page-hero h1,.page-hero p{color:#111}.panel{box-shadow:none}.section{padding:12px 0}}
/* Allow internally scrollable scientific diagrams to shrink inside CSS grid cells. */
.content-layout > *, .lab-two > *, .panel, .periodic-scroll{min-width:0}
.periodic-scroll{width:100%}