:root{color-scheme:light;--bg:#fff;--surface:#f6f8fa;--card:#fff;--text:#20262e;--muted:#687582;--subtle:#89949e;--line:#e6ebef;--blue:#087bed;--teal:#168c8a;--purple:#8870c1;--nav:#f7f9fb;--softblue:#eaf3fe;--glass:rgba(255,255,255,.86);--shadow:0 16px 55px #1a344909;--sidebar:238px;--ease:cubic-bezier(.22,1,.36,1);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Microsoft YaHei",sans-serif;font-size:15px;line-height:1.65;font-synthesis:none;scroll-behavior:smooth;scroll-padding-top:92px}
:root[data-theme=dark]{color-scheme:dark;--bg:#12171d;--surface:#191f27;--card:#1a2028;--text:#edf2f7;--muted:#a6b1bf;--subtle:#8b99aa;--line:#303946;--blue:#63acff;--teal:#58c3bc;--purple:#b69ae9;--nav:#151b22;--softblue:#24364d;--glass:rgba(18,23,29,.88);--shadow:0 16px 55px #0002}
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svg{width:19px;height:19px;stroke:currentColor;fill:none;stroke-width:1.6;stroke-linecap:round;stroke-linejoin:round}h1,h2,h3,p{margin:0}h1,h2,h3{font-weight:650}h2{font-size:clamp(25px,2.45vw,33px);letter-spacing:-.055em;line-height:1.4}h3{line-height:1.45;letter-spacing:-.025em}p{color:var(--muted)}[hidden]{display:none!important}.sr-only{position:absolute;width:1px;height:1px;padding:0;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap}.skip-link{position:fixed;left:20px;top:-100px;background:var(--card);z-index:30;padding:10px 20px}.skip-link:focus{top:10px}.topbar{height:65px;position:fixed;top:0;inset-inline:0;z-index:20;display:flex;align-items:center;justify-content:space-between;padding:0 31px;background:var(--glass);backdrop-filter:blur(24px) saturate(160%);border-bottom:1px solid var(--line)}.brand{display:flex;align-items:center;gap:11px;white-space:nowrap}.brand>svg{width:28px;height:28px;stroke:var(--blue);fill:none;stroke-width:2;stroke-linecap:round}.brand 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var(--line);background:var(--card);border-radius:13px;--city:var(--blue)}.metric-card.shanghai{--city:var(--teal)}.metric-card.harbin{--city:var(--purple)}.city-heading{display:flex;align-items:center;justify-content:space-between;font-size:12px;font-weight:600}.city-heading small{color:var(--subtle);font-size:8px;letter-spacing:.11em;font-weight:400}.city-dot,.city-toggles i,.donut-legend i,.quality-legend i,.season-key i{display:inline-block;width:6px;height:6px;background:var(--city);border-radius:50%;margin-right:7px}.metric-value{display:flex;align-items:baseline;font-size:42px;line-height:1.2;font-weight:600;letter-spacing:-.06em;color:var(--city);margin-top:17px}.metric-value>span{font-size:22px;font-weight:450;margin-left:3px}.metric-value svg{width:65px;height:30px;margin-left:auto;fill:none;stroke:var(--city);stroke-width:1.8}.metric-card p{font-size:10px;margin-top:8px}.metric-baseline{font-size:12px;margin-top:16px;border-top:1px solid 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strong{font-weight:600;color:var(--text)}.data-details{border-bottom:1px solid var(--line);font-size:12px}.data-details>summary{padding:13px 0;cursor:pointer;color:var(--blue)}.data-details>summary>span{font-size:10px;color:var(--subtle);float:right}.table-controls{display:flex;align-items:center;justify-content:space-between;padding:15px 0}.table-controls select{margin-left:10px;font-size:11px;background:var(--card);border:1px solid var(--line);padding:5px;border-radius:5px}.table-scroll{overflow:auto;max-height:440px}table{border-collapse:collapse;width:100%;font-size:11px;font-variant-numeric:tabular-nums;text-align:left}th{font-weight:500;color:var(--muted)}td,th{padding:11px 14px;border-bottom:1px solid var(--line);white-space:nowrap}thead th{background:var(--surface);position:sticky;top:0}caption{text-align:left;font-size:10px;color:var(--muted);padding:8px 0}.table-note,.section-footnote{font-size:10px;line-height:1.9;color:var(--muted);margin-top:15px}.table-note{padding-bottom:20px}.pollutant-tabs{display:flex;border-bottom:1px solid var(--line);padding:0 25px;gap:23px;overflow:auto}.pollutant-tabs button{padding:16px 5px 13px;font-size:12px;color:var(--muted);position:relative;white-space:nowrap}.pollutant-tabs button:after{content:"";position:absolute;bottom:-1px;height:2px;left:4px;right:4px;background:var(--blue);transform:scaleX(0);transition:transform .3s var(--ease)}.pollutant-tabs .selected{color:var(--blue);font-weight:600}.pollutant-tabs .selected:after{transform:scaleX(1)}.pollutant-content{display:grid;grid-template-columns:.8fr 1.2fr;gap:50px;padding:33px 32px;min-height:250px}.small-label{font-size:10px;color:var(--subtle);letter-spacing:.06em}.pollutant-explainer h3{font-size:23px;margin-top:7px}.pollutant-explainer>p{font-size:11px;margin-top:5px}.unit-chip{display:inline-block;margin:12px 0 0;padding:3px 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span{font-size:10px;color:var(--subtle)}.change-matrix{text-align:center;border-collapse:separate;border-spacing:5px;font-size:11px}.change-matrix th,.change-matrix td{border:0;padding:11px 9px;border-radius:5px}.change-matrix thead th{background:none;font-size:10px}.change-matrix tbody td{background:#eaf5f2;color:#217a65}.change-matrix tbody th{text-align:left;color:var(--text)}.change-matrix td.rise{background:#fcf0df;color:#9a6a28}.change-matrix td.missing{background:var(--surface);color:var(--subtle)}[data-theme=dark] .change-matrix tbody td{background:#203932;color:#95d9c0}[data-theme=dark] .change-matrix td.rise{background:#403121;color:#e9bf82}[data-theme=dark] .change-matrix td.missing{background:var(--surface);color:var(--subtle)}.story-grid{display:grid;grid-template-columns:1fr 1fr;gap:20px}.story-card{border:1px solid var(--line);border-radius:13px;padding:27px;background:var(--card)}.story-card h3{font-size:21px;margin:8px 0 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100%);padding:23px;transform:rotate(-90deg);flex-shrink:0}.donut>div{border-radius:50%;background:var(--card);height:100%;display:flex;flex-direction:column;align-items:center;justify-content:center;transform:rotate(90deg)}.donut strong{font-size:35px;font-weight:550;line-height:1.2}.donut div span{font-size:10px;color:var(--muted);margin-top:5px}.donut-legend p{font-size:11px;color:var(--text);margin:10px 0}.donut-legend strong{display:block;font-size:19px;font-weight:550;padding-left:13px;margin-top:4px;white-space:nowrap}.donut-legend small{font-size:10px;font-weight:400}.donut-legend p>span{display:block;color:var(--muted);font-size:10px;margin-left:13px}.quality-panel{margin-top:20px;padding-bottom:21px}.quality-panel .section-footnote{margin-inline:26px}.quality-row{display:grid;grid-template-columns:45px 1fr;align-items:center;gap:15px;font-size:11px;margin:17px 26px}.quality-stack{display:flex;height:32px;gap:2px;border-radius:4px;overflow:hidden}.quality-stack span{display:flex;align-items:center;justify-content:center;font-size:10px;color:#1b3b32;min-width:3px;font-variant-numeric:tabular-nums}.quality-legend{display:flex;justify-content:center;flex-wrap:wrap;gap:18px;font-size:9px;color:var(--muted);margin:20px 26px}.context-feature{display:grid;grid-template-columns:1.15fr 1fr;background:var(--surface);border-radius:17px;margin-top:26px;padding:36px;gap:45px}.context-badge{font-size:10px;background:var(--card);padding:5px 9px;border:1px solid var(--line);border-radius:5px;color:var(--muted)}.context-copy h3{font-size:24px;line-height:1.5;margin:18px 0 16px}.context-copy p{font-size:12px;line-height:1.9}.context-copy p strong{color:var(--text);font-weight:600}.context-copy p.context-caution{font-size:10px;margin-top:14px}.context-copy .text-link{margin-top:18px}.season-chart{align-self:center}.season-key{display:flex;gap:18px;font-size:9px;color:var(--muted);margin:9px 0 26px}.season-pair{display:grid;grid-template-columns:45px 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