:root{color-scheme:light;--bg:#f5fbfc;--ink:#17323a;--muted:#607d88;--teal:#0ba99b;--darkteal:#087c71;--blue:#2888da;--line:#d7e9ed;--soft:#e9f8f6;--good:#0e9167;--warn:#af7204;--danger:#bf3947;--shadow:0 12px 34px rgba(43,92,105,.065)}
*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:110px}body{margin:0;background:var(--bg);font-family:Inter,ui-sans-serif,system-ui,-apple-system,"Segoe UI",sans-serif;color:var(--ink);font-size:15px;line-height:1.62}button,input{font:inherit}button{cursor:pointer}a{color:#007e75}a:hover{color:#005f58}strong{font-weight:760}h1,h2,h3,p{margin-top:0}h1{font-size:clamp(36px,5vw,57px);letter-spacing:-2px;line-height:1.10;margin-bottom:18px}h2{letter-spacing:-.6px;font-size:clamp(23px,3vw,29px);line-height:1.2}h3{font-size:17px;letter-spacing:-.25px;line-height:1.25}p{color:#4e6b75}ul{padding-left:21px;margin:10px 0}li+li{margin-top:6px}*:focus-visible{outline:3px solid rgba(10,169,155,.4);outline-offset:3px}
.topbar{position:sticky;top:0;z-index:20;background:rgba(255,255,255,.96);backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}.nav{max-width:1220px;margin:auto;min-height:75px;padding:8px 22px;display:flex;align-items:center;justify-content:space-between;gap:18px}.brand{display:flex;align-items:center;min-width:0}.brand img{width:clamp(230px,28vw,325px);height:auto;display:block}.site-links{display:flex;gap:8px;align-items:center;flex-wrap:wrap}.site-links a{color:#42616a;text-decoration:none;padding:9px 14px;border-radius:12px;white-space:nowrap;font-weight:750;font-size:14px}.site-links a.active{background:#e6f7f3;color:#087f74}.site-links a:hover{background:#f0faf8;color:#087f74}
.demo-ribbon{text-align:center;padding:8px 14px;background:#eaf5ff;color:#355f78;font-size:12px;border-bottom:1px solid #d1e5f3;font-weight:600}.demo-ribbon strong{color:#22516b}
.hero{position:relative;max-width:1200px;margin:auto;padding:53px 22px 34px;display:grid;grid-template-columns:1.18fr .82fr;align-items:center;gap:30px}.eyebrow{font-size:11px;text-transform:uppercase;letter-spacing:.15em;font-weight:850;color:#077c74;margin:0 0 15px;display:flex;align-items:center;gap:8px}.eyebrow:before{content:"";width:8px;height:8px;border-radius:50%;background:#19c0af}.hero h1 span{color:var(--teal)}.hero p{font-size:17px;line-height:1.72;max-width:610px;margin-bottom:23px}.hero-actions{display:flex;align-items:center;flex-wrap:wrap;gap:10px}.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;border:1px solid transparent;border-radius:12px;text-decoration:none;font-size:14px;font-weight:800;padding:12px 17px;line-height:1.3;transition:transform .15s,box-shadow .15s}.btn:hover{transform:translateY(-1px)}.btn.primary{color:white;background:linear-gradient(110deg,#0cae9d,#26bba9);box-shadow:0 7px 16px rgba(10,169,155,.16)}.btn.ghost{border-color:#d1e6e7;background:white;color:#146d67}.fineprint{font-size:12px;color:#759099;margin-top:16px}.hero-art{background:linear-gradient(135deg,#dbf8f1,#eff8ff 80%);border:1px solid #c7e7e5;border-radius:28px;min-height:320px;padding:27px;position:relative;overflow:hidden;box-shadow:var(--shadow)}.hero-art:before,.hero-art:after{content:"";position:absolute;border-radius:50%;border:1px solid rgba(5,128,140,.09)}.hero-art:before{width:320px;height:320px;right:-125px;top:-150px}.hero-art:after{width:245px;height:245px;left:-115px;bottom:-130px}.art-caption{display:flex;align-items:center;justify-content:space-between;gap:10px;position:relative;z-index:1}.art-caption strong{font-size:13px;color:#2f6872}.art-caption span{font-size:11px;color:#579199;background:rgba(255,255,255,.62);border:1px solid rgba(255,255,255,.5);padding:5px 10px;border-radius:30px}.art-step{position:relative;z-index:1;background:white;border:1px solid #d3e9ec;padding:13px 15px;border-radius:14px;display:flex;align-items:center;gap:12px;box-shadow:0 5px 14px rgba(42,106,116,.05)}.art-step+ .art-arrow{position:relative;z-index:1;text-align:center;color:#45ada6;font-size:20px;font-weight:700;line-height:1.05;height:22px}.art-step:first-of-type{margin-top:20px}.art-dot{width:38px;height:38px;border-radius:12px;display:grid;place-items:center;font-weight:850;font-size:12px;flex:none}.art-red{background:#ffe5e4;color:#b33a40}.art-yellow{background:#fff4db;color:#9c6c07}.art-green{background:#e5f7ed;color:#0b8553}.art-step b{display:block;font-size:14px}.art-step small{color:#708891;font-size:12px}.art-footer{margin:14px 0 0;font-size:12px;color:#567981;position:relative;z-index:1}
.page{max-width:1200px;margin:auto;padding:0 22px 70px}.facts{display:grid;grid-template-columns:repeat(3,1fr);gap:13px;margin-bottom:25px}.fact{background:#fff;border:1px solid var(--line);border-radius:17px;padding:17px 18px;display:flex;align-items:center;gap:13px}.fact-icon{width:40px;height:40px;flex:none;display:grid;place-items:center;background:#eaf8f6;border-radius:13px;font-size:19px}.fact b{display:block;font-size:14px}.fact span{display:block;color:var(--muted);font-size:12px}
.main-grid{display:grid;grid-template-columns:220px minmax(0,1fr);align-items:start;gap:22px}.toc{position:sticky;top:110px;background:white;border:1px solid var(--line);border-radius:20px;padding:19px 13px;box-shadow:var(--shadow)}.toc h2{font-size:12px;letter-spacing:.1em;text-transform:uppercase;color:#50717b;margin:0 10px 12px}.toc a{display:block;text-decoration:none;font-size:13px;color:#54737d;font-weight:700;padding:9px 12px;border-radius:9px}.toc a:hover,.toc a.active{background:#e9f8f6;color:#067b71}.toc-note{border-top:1px solid #e6eff1;margin-top:11px;padding:14px 10px 2px;color:#6a848d;font-size:12px;line-height:1.55}.main-content{min-width:0;display:grid;gap:21px}.panel{background:white;border:1px solid var(--line);border-radius:22px;padding:clamp(20px,3vw,29px);box-shadow:var(--shadow)}.section-kicker{font-size:11px;text-transform:uppercase;letter-spacing:.12em;color:#0b8f83;font-weight:850;margin-bottom:9px}.section-intro{max-width:650px;color:#63808b;font-size:14px;line-height:1.7;margin-bottom:18px}.flow{display:grid;grid-template-columns:1fr 20px 1fr 20px 1fr;gap:10px;align-items:center;margin:20px 0 16px}.chem{border-radius:16px;padding:18px 14px;border:1px solid;min-height:130px}.chem b{font-size:15px;display:block}.chem .symbol{font-size:27px;font-weight:850;letter-spacing:-1px;margin:4px 0}.chem span{font-size:11px;display:block;color:#596f76}.chem.red{background:#fff3f3;border-color:#f1d4d5;color:#a83441}.chem.yellow{background:#fff9ea;border-color:#f2e3bc;color:#91630a}.chem.green{background:#f0fcf5;border-color:#cbebd6;color:#0b7f52}.chem-arrow{font-size:24px;color:#7ab4b6;text-align:center;font-weight:500}.explain{background:#f4fafb;border:1px solid #dcecef;border-radius:13px;padding:14px 16px;font-size:13px;color:#52717b;line-height:1.6}.explain strong{color:#214e57}
.step-list{display:grid;gap:10px}.step{display:grid;grid-template-columns:38px 1fr;gap:13px;background:#fbfefe;border:1px solid #e0edf0;border-radius:15px;padding:15px}.step-num{display:grid;place-items:center;width:35px;height:35px;background:#e5f7f3;border-radius:12px;color:#087d73;font-weight:850}.step h3{margin-bottom:5px}.step p{margin:0;font-size:13px;line-height:1.7}.split-chips{display:flex;flex-wrap:wrap;gap:6px;margin:10px 0 0}.chip{border:1px solid #d2e5e9;background:#f4fafb;padding:5px 10px;border-radius:30px;font-size:11px;color:#456874;font-weight:720}.chip.good{color:#0b7b58;background:#eaf8f0;border-color:#bee3cc}.chip.warn{color:#9b6500;background:#fff8e4;border-color:#f1dca9}.chip.bad{color:#ac3140;background:#fff1f1;border-color:#efc7ca}
.mode-switch{display:grid;grid-template-columns:1fr 1fr;gap:8px;background:#eef8f8;border:1px solid #dce9ea;border-radius:15px;padding:6px;margin:16px 0}.mode-btn{color:#3f6970;font-size:13px;font-weight:800;border:0;border-radius:11px;background:transparent;padding:11px 12px;box-shadow:none}.mode-btn[aria-selected="true"]{background:white;color:#078578;box-shadow:0 3px 8px rgba(14,96,102,.1)}[hidden]{display:none!important}.note-box{border:1px solid #c8e7df;border-left:4px solid #22ab92;background:#f1faf7;border-radius:13px;padding:13px 15px;font-size:13px;color:#406d68;line-height:1.65}.note-box.warn{background:#fffbf0;border-color:#f1d7a5;border-left-color:#e5a522;color:#795c26}.note-box.danger{background:#fff6f6;border-color:#f0ced1;border-left-color:#cd4b52;color:#82484a}.note-box b{color:#243f46}.mini-title{margin:18px 0 7px;font-weight:850;color:#21434b;font-size:14px}
.tracker-form{border:1px solid #dcebed;border-radius:17px;padding:17px;background:#fbfefe;margin-top:15px}.test-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:11px}.test-field label{font-size:12px;font-weight:800;color:#476e79;display:block;margin-bottom:5px}.test-field small{display:block;font-weight:500;color:#8aa0a8;font-size:11px}.test-field input{padding:11px 12px;width:100%;border:1px solid #cbdfe4;border-radius:11px;background:white;color:#17323a;appearance:textfield}.test-field input:focus{border-color:var(--teal);outline:3px solid #c7f2ed}.test-field input[aria-invalid=true]{border-color:#c94451}.checkbox-row{display:flex;align-items:flex-start;gap:10px;padding:12px;border:1px solid #e1ecee;border-radius:13px;background:#fff;font-size:13px;margin-top:11px}.checkbox-row input{width:17px;height:17px;accent-color:#0cae9d;margin:2px 0 0;flex:none}.checkbox-row label{cursor:pointer;color:#486972}.tracker-actions{display:flex;gap:9px;flex-wrap:wrap;margin-top:12px}.tracker-actions button{border:0;padding:11px 16px;border-radius:11px;background:#0cae9d;color:white;font-size:13px;font-weight:800}.tracker-actions .secondary{background:#eef8f7;color:#157e74;border:1px solid #cae8e3}.tracker-result{margin-top:13px;padding:15px;border-radius:14px;border:1px solid #d6e8ed;background:white}.tracker-result h3{margin-bottom:5px}.tracker-result p{font-size:13px;margin-bottom:0}.tracker-result.good{border-color:#b4e5ce;background:#f0fcf5}.tracker-result.warn{border-color:#e9d49d;background:#fffbf0}.tracker-result.bad{border-color:#efbdc4;background:#fff5f5}.tracker-result.neutral{border-color:#d7e9ed;background:#f4fafc}.tracker-result .result-pill{display:inline-flex;margin-bottom:7px;font-size:10px;letter-spacing:.065em;text-transform:uppercase;font-weight:850;color:#327a7f}.tracker-result.good .result-pill{color:#09865c}.tracker-result.warn .result-pill{color:#ab7107}.tracker-result.bad .result-pill{color:#ba404a}
.checklist{display:grid;gap:8px;margin-top:14px}.task{display:flex;gap:11px;align-items:flex-start;padding:11px 13px;border:1px solid #e3edef;border-radius:12px;font-size:13px;line-height:1.55;background:#fbfefe}.task input{margin-top:3px;width:17px;height:17px;accent-color:var(--teal);flex:none}.task label{cursor:pointer}.check-progress{display:flex;align-items:center;gap:12px;margin-top:15px}.bar{height:9px;border-radius:99px;background:#e6f0f2;flex:1;overflow:hidden}.bar div{height:100%;width:0;background:linear-gradient(90deg,#0cae9d,#298bdf);border-radius:99px;transition:width .2s}.check-progress span{font-size:12px;color:#567a83;font-weight:800}.tip-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:11px}.tip{padding:15px;border:1px solid #deebed;border-radius:15px;background:#fbfefe}.tip b{display:block;font-size:13px;margin-bottom:5px}.tip p{font-size:12px;margin:0;line-height:1.7}details{border:1px solid #dce9ed;border-radius:13px;padding:0 15px;background:#fbfefe}details+details{margin-top:9px}summary{font-size:14px;font-weight:780;cursor:pointer;padding:14px 4px;list-style-position:outside}details p{font-size:13px;margin:0;padding:0 3px 15px;line-height:1.7}.footer{border-top:1px solid #deeaed;padding:24px 22px 36px;color:#7a939a;font-size:12px;max-width:1200px;margin:auto}.footer a{color:#0b8175}.footer-inner{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap}.preview-badge{font-size:11px;border-radius:40px;background:#ecf8f5;color:#09897a;border:1px solid #c4e8df;padding:5px 11px;font-weight:760}
@media(max-width:1050px){.hero{grid-template-columns:1fr .84fr;gap:15px}.hero-art{min-height:300px;padding:19px}.main-grid{grid-template-columns:190px minmax(0,1fr)}}
@media(max-width:820px){.hero{grid-template-columns:1fr;padding-top:36px}.hero-art{min-height:auto;max-width:650px}.main-grid{grid-template-columns:1fr}.toc{position:static;display:flex;align-items:center;overflow-x:auto;gap:4px;padding:9px}.toc h2,.toc-note{display:none}.toc a{white-space:nowrap}.facts{grid-template-columns:repeat(3,1fr)}.flow{gap:6px}}
@media(max-width:560px){.nav{flex-direction:column;align-items:flex-start;padding:10px 14px;gap:4px}.brand img{width:min(292px,83vw)}.site-links{gap:3px}.site-links a{padding:6px 9px;font-size:12px}.hero{padding:32px 17px 24px}.hero h1{font-size:37px}.hero p{font-size:15px}.page{padding:0 13px 45px}.facts{grid-template-columns:1fr;gap:8px}.fact{padding:11px 14px}.panel{padding:19px 15px}.flow{grid-template-columns:1fr;gap:7px}.chem{min-height:auto;padding:13px}.chem-arrow{transform:rotate(90deg);height:27px}.test-grid{grid-template-columns:1fr}.tip-grid{grid-template-columns:1fr}.mode-switch{grid-template-columns:1fr}.step{grid-template-columns:32px 1fr;gap:9px}.step-num{width:31px;height:31px}.art-step{padding:10px}.fact-icon{height:35px;width:35px}.footer{padding:17px}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{transition:none!important}}

/* Published guide: consistent desktop and mobile site navigation. */
.site-links a[aria-current="page"]{background:#e9f8f6;color:#087f74}
@media (min-width:561px) and (max-width:680px){.nav{flex-wrap:wrap}.brand img{width:250px}}
@media(max-width:560px){.site-links{gap:8px}.site-links a{font-size:14px;padding:7px 11px}}

/* Tank cycling FAQs: a tidy stationary dot rather than native disclosure triangles. */
#questions details summary {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 15px 5px;
  list-style: none;
  list-style-type: none;
  line-height: 1.5;
}
#questions details summary::-webkit-details-marker { display: none; }
#questions details summary::marker { content: ""; }
#questions details summary::before {
  content: "";
  width: 7px;
  height: 7px;
  margin-top: 0;
  border-radius: 50%;
  background: #0a9c8f;
  flex: 0 0 7px;
  align-self: center;
}
#questions details[open] summary::before { background: #087c76; }
#questions details p {
  padding: 0 7px 17px 24px;
  margin: 0;
  line-height: 1.75;
}
@media (max-width: 560px) {
  #questions details summary { gap: 10px; padding: 13px 2px; }
  #questions details p { padding-left: 19px; padding-right: 2px; }
}