.spf-paper{background:#fff!important;color:#193653!important}.spf-paper>.transport,.spf-paper>.drawing-viewport,.spf-paper>.step-caption{display:none!important}.spf-lesson{--spf-blue:#245bce;--spf-ink:#193653;padding:24px;color:var(--spf-ink);font:16px/1.5 system-ui,sans-serif}.spf-lesson *{box-sizing:border-box}.spf-lesson h2{font:600 24px/1.3 system-ui;margin:8px 0 20px}.spf-lesson h3{font:650 17px/1.4 system-ui;margin:6px 0}.spf-eyebrow{font-size:12px;letter-spacing:.13em;color:#49627d}.spf-controls{display:flex;flex-wrap:wrap;gap:8px}.spf-lesson button{font:inherit;color:var(--spf-ink);border:1px solid #8095ad;border-radius:7px;background:#fff;min-height:44px;padding:8px 14px;cursor:pointer}.spf-lesson button:disabled{opacity:.5;cursor:default}.spf-lesson :focus-visible{outline:3px solid #245bce;outline-offset:3px}.spf-caption{padding:16px 0;min-height:110px}.spf-caption p{margin:4px 0}.spf-map{display:grid;grid-template-columns:minmax(0,1fr) minmax(160px,.85fr) minmax(0,1.25fr);gap:16px;align-items:center}.spf-actor{border:1.5px solid #93abc5;border-radius:14px;padding:16px;text-align:center;background:#f5f8fc;min-width:0}.spf-actor>svg{height:62px;width:70px;display:block;margin:auto}.spf-actor span,.spf-actor strong,.spf-actor b{display:block}.spf-ip{font-size:22px;color:#245bce}.spf-flow{text-align:center;color:#49627d;font-size:14px;min-width:0}.spf-smtp>span:first-child{display:block;border-bottom:3px solid #245bce;color:#245bce;font-weight:650;padding-bottom:4px}.spf-moving svg{width:65px;height:40px}.spf-lesson code{font:14px/1.6 ui-monospace,monospace;overflow-wrap:anywhere}.spf-lesson mark{background:#e1ebff;color:#17439e;padding:1px 3px;border-radius:3px}.spf-extract{display:block;margin-top:6px}.spf-dns-flow{grid-column:3;display:flex;justify-content:space-around;gap:12px}.spf-request,.spf-response{border-left:2px solid #245bce;padding-left:8px;color:#245bce;flex:1}.spf-dns{grid-column:3;grid-row:3}.spf-policy{display:block;margin:12px 0;padding:10px;background:#fff;border:1px solid #bac9d9;border-radius:6px}.spf-policy strong{display:inline;color:#206443}.spf-dns dl{margin:10px 0;font-size:13px;text-align:left}.spf-dns dl div{margin:7px 0}.spf-dns dt{font-family:monospace;font-weight:650}.spf-dns dd{margin:0}.spf-decision{grid-column:1/3;grid-row:3;align-self:center;border:1.5px solid #93abc5;border-radius:14px;padding:16px;position:relative}.spf-decision:after{content:'← DNS answer to receiver';position:absolute;right:8px;top:-28px;font-size:13px;color:#245bce}.spf-compare{display:flex;align-items:center;justify-content:space-around;gap:8px;text-align:center}.spf-compare span,.spf-compare strong{display:block}.spf-compare span{font-size:13px}.spf-compare strong{font-size:18px}.spf-compare>b{font-size:28px}.spf-result{padding:14px;margin:16px 0 8px;text-align:center;border-radius:8px;border:1px solid}.spf-result strong,.spf-result span{display:block}.spf-pass{background:#ebf7ee;color:#17623b}.spf-fail{background:#fff0ee;color:#9c2922}.spf-pending{background:#f5f8fc;color:#49627d}.spf-active{border-color:#245bce;box-shadow:0 0 0 2px #e1ebff}.spf-map> :not(.spf-active){opacity:.78}.spf-decision small,.spf-dns small{font-size:12px}.spf-experiment{margin:28px 0 16px;padding:14px;border:1px solid #a6b7ca;border-radius:8px}.spf-experiment label{display:inline-flex;align-items:center;min-height:44px;margin-right:20px;gap:6px}.spf-experiment p{font-size:14px;margin:8px 0 0}.spf-takeaway{padding:14px;border-left:3px solid #245bce;background:#f1f6ff}.spf-identities{margin-top:30px}.spf-identity-grid{display:grid;grid-template-columns:1fr 1fr;gap:16px}.spf-identity-grid>button{display:flex;flex-direction:column;align-items:center;gap:10px;text-align:center;overflow-wrap:anywhere;padding:18px}.spf-identity-grid svg{height:75px;width:140px}.spf-identity-grid [aria-pressed=true]{border:2px solid #245bce;background:#f1f6ff}.spf-identity-grid strong{font-size:14px}.spf-envelope strong{color:#17623b}.spf-identity-answer{min-height:72px}.spf-advanced{border:1px solid #a6b7ca;border-radius:9px;padding:16px;margin-top:24px}.spf-advanced summary{cursor:pointer;font-weight:650;min-height:44px}.spf-advanced article{border-top:2px solid #93abc5;padding-top:12px}.spf-citations{display:flex;flex-wrap:wrap;gap:14px;font-size:13px}.spf-citations a{color:#17439e;text-decoration:underline;min-height:30px}.spf-lesson[data-playing=true] .spf-active .spf-moving{animation:spf-mail 1.4s ease-in-out infinite}.spf-lesson[data-step="2"] .spf-active .spf-request{animation:spf-query 2s both}.spf-lesson[data-step="2"] .spf-active .spf-response{animation:spf-query 2s 2s both}.spf-lesson[data-step='3'] .spf-result{animation:spf-query .4s both}@keyframes spf-mail{from{transform:translateX(-20px)}to{transform:translateX(20px)}}@keyframes spf-query{from{opacity:.25;transform:translateY(-5px)}to{opacity:1;transform:none}}@media(max-width:1000px){.spf-map{grid-template-columns:minmax(0,1fr) minmax(110px,.65fr) minmax(0,1fr);gap:12px}.spf-lesson{padding:18px}.spf-compare{flex-wrap:wrap}}@media(max-width:1100px){.spf-map{display:flex;flex-direction:column;align-items:stretch;gap:18px}.spf-sender{order:0}.spf-smtp{order:1}.spf-receiver{order:2}.spf-dns-flow{order:3}.spf-dns{order:4}.spf-decision{order:5;margin-top:18px}.spf-smtp>span:first-child{border:0}.spf-smtp>span:first-child:after{content:' ↓';display:block;font-size:24px}.spf-decision:after{content:'↓ DNS answer → receiver compares';right:auto;left:8px}.spf-identity-grid{grid-template-columns:1fr}.spf-caption{min-height:140px}.spf-lesson h2{font-size:21px}.spf-lesson{padding:16px}.spf-compare strong{font-size:16px}.spf-controls button{flex:1;padding:8px}.spf-identity-answer{min-height:100px}}@media(prefers-reduced-motion:reduce){.spf-lesson *{animation:none!important;transition:none!important}}
/* Attach flow lines to the actors rather than leave arrows floating in space. */
.spf-smtp{position:relative}.spf-smtp>span:first-child{position:relative;margin:0 -16px}.spf-smtp>span:first-child:after{content:'';position:absolute;right:0;bottom:-7px;width:11px;height:11px;border-right:3px solid #245bce;border-top:3px solid #245bce;transform:rotate(45deg)}.spf-dns-flow{align-self:stretch;margin:-16px 0;min-height:90px}.spf-request,.spf-response{position:relative;display:flex;flex-direction:column;justify-content:center;margin:0 12px;border-left-width:3px}.spf-request:after,.spf-response:after{content:'';position:absolute;left:-7px;width:11px;height:11px;border-right:3px solid #245bce;border-bottom:3px solid #245bce}.spf-request:after{bottom:0;transform:rotate(45deg)}.spf-response:after{top:0;transform:rotate(225deg)}.spf-decision:before{content:'';position:absolute;right:-18px;top:50%;width:16px;border-top:3px solid #245bce}.spf-map> :not(.spf-active){opacity:1}.spf-lesson[data-step='1'] .spf-extract{animation:spf-query .6s both}.spf-map>div:not(.spf-active){border-color:#b5c5d7}.spf-map>.spf-active{background-color:#eef4ff}.spf-decision.spf-active .spf-result{background-color:#ebf7ee}.spf-decision.spf-active .spf-fail{background-color:#fff0ee}@media(max-width:1000px){.spf-smtp>span:first-child{margin:0 -12px}}@media(max-width:1100px){.spf-smtp>span:first-child{margin:0}.spf-smtp>span:first-child:after{content:'↓';position:static;display:block;width:auto;height:auto;border:0;transform:none}.spf-dns-flow{margin:-18px 0;min-height:110px}.spf-decision:before{top:-20px;right:50%;height:18px;width:0;border-top:0;border-left:3px solid #245bce}.spf-decision:after{top:-34px;background:white;padding:0 5px}.spf-decision{margin-top:28px}}

.spf-policy>span{display:inline}.spf-policy{white-space:normal}
/* This lesson reflows as a document instead of the shared fixed-height SVG stage. */
.spf-reader .reader-stage{height:auto;min-height:0;display:block}.spf-reader .reader-stage>.paper{display:block;flex:none;overflow:visible}.spf-reader .spf-paper{border:1px solid #bac9d9;border-radius:12px}.spf-reader .spf-paper .paper-header{border-radius:12px 12px 0 0}