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16px;display:flex}.free-banner-icon{flex-shrink:0;font-size:1.2rem}.free-banner-text{color:#34d399;font-size:.8rem;line-height:1.5}.paywall-overlay{z-index:300;-webkit-backdrop-filter:blur(8px);backdrop-filter:blur(8px);background:#000000bf;align-items:flex-end;display:none;position:fixed;inset:0}.paywall-overlay.show{display:flex}.paywall-sheet{background:var(--surface);border-top:1px solid var(--border);border-radius:28px 28px 0 0;width:100%;max-height:92vh;padding-bottom:40px;animation:.35s cubic-bezier(.34,1.56,.64,1) slideUp;overflow-y:auto}@keyframes slideUp{0%{transform:translateY(100%)}to{transform:none}}.paywall-handle{background:var(--border);border-radius:2px;width:40px;height:4px;margin:14px auto 0}.paywall-head{text-align:center;padding:20px 24px 4px}.paywall-icon{margin-bottom:10px;font-size:2.2rem}.paywall-title{letter-spacing:-.5px;margin-bottom:6px;font-size:1.2rem;font-weight:800}.paywall-sub{color:var(--muted);margin-bottom:20px;font-size:.8rem;line-height:1.5}.plan-cards{flex-direction:column;gap:10px;padding:0 20px 16px;display:flex}.plan-card{background:var(--card);border:2px solid var(--border);cursor:pointer;border-radius:18px;padding:16px 18px;transition:all .2s;position:relative}.plan-card.selected{border-color:var(--accent);background:#00d4ff0d}.plan-card.popular:after{content:"BEST VALUE";letter-spacing:1.5px;background:linear-gradient(135deg,var(--accent2),var(--accent));color:#fff;border-radius:20px;padding:3px 10px;font-size:.58rem;font-weight:700;position:absolute;top:-10px;right:14px}.plan-row{justify-content:space-between;align-items:center;display:flex}.plan-name{font-size:.95rem;font-weight:700}.plan-price{font-family:var(--mono);color:var(--accent);font-size:1.15rem;font-weight:700}.plan-price small{color:var(--muted);font-size:.7rem;font-family:var(--font);font-weight:400}.plan-desc{color:var(--muted);margin-top:3px;font-size:.75rem}.plan-save{color:var(--accent3);margin-top:2px;font-size:.68rem;font-weight:700}.paywall-cta{background:linear-gradient(135deg,var(--accent2),var(--accent));font-family:var(--font);color:#fff;cursor:pointer;text-align:center;appearance:none;border:none;border-radius:16px;justify-content:center;align-items:center;gap:10px;width:calc(100% - 40px);margin:0 20px 8px;padding:16px;font-size:1rem;font-weight:700;display:flex}.paywall-cta:disabled{opacity:.9;cursor:wait}.paywall-cta-spinner{border:2px solid #ffffff59;border-top-color:#fff;border-radius:50%;flex-shrink:0;width:1.125rem;height:1.125rem;animation:.7s linear infinite paywall-cta-spin}@keyframes paywall-cta-spin{to{transform:rotate(360deg)}}.paywall-dismiss{text-align:center;color:var(--muted);cursor:pointer;padding:10px;font-size:.78rem;display:block}.trial-note{text-align:center;color:var(--muted);padding:0 24px 16px;font-size:.72rem;line-height:1.5}.profile-menu{top:68px;right:var(--content-pad-inline);z-index:200;background:var(--card);border:1px solid var(--border);border-radius:18px;min-width:200px;padding:8px;display:none;position:fixed;box-shadow:0 20px 60px #00000080}.profile-menu.show{animation:.15s fadeIn;display:block}.pm-header{border-bottom:1px solid var(--border);margin-bottom:6px;padding:12px 14px 10px}.pm-name{color:var(--text);font-size:.9rem;font-weight:700}.pm-email{color:var(--muted);font-size:.72rem}.pm-item{cursor:pointer;color:var(--text);border-radius:12px;align-items:center;gap:10px;padding:10px 14px;font-size:.85rem;transition:background .15s;display:flex}.pm-item:hover{background:#ffffff0a}.pm-item.danger{color:#f87171}.profile-menu .pm-item{font:inherit;appearance:none;background:0 0;border:none;transition:background .15s}.profile-menu button.pm-item{text-align:left;width:100%}.profile-menu .pm-item.danger{color:#f87171}.profile-menu .pm-item:hover,.profile-menu .pm-item:focus-visible{background:#ffffff0a}.profile-menu .pm-item.danger:hover,.profile-menu .pm-item.danger:focus-visible{color:#f87171;background:#ffffff0a}mjx-container{max-width:100%;overflow:visible}mjx-container:not([display=true]){vertical-align:baseline;display:inline-block}mjx-container[display=true]{padding:4px 0;display:block;overflow-x:visible}.math-box mjx-container{max-width:none;display:inline-block}.math-box{white-space:nowrap;padding-right:8px}.MathJax{font-size:1em!important}.q-statement mjx-container,.step-text mjx-container,.step-label mjx-container,.answer-block .aval mjx-container,.q-statement .MathJax,.step-text .MathJax,.step-label .MathJax,.answer-block .aval .MathJax{font-size:1.12em!important}mjx-mfrac{font-size:.94em!important}mjx-line{margin-top:0!important;margin-bottom:0!important}mjx-den{margin-top:-.1em!important}.vtight mjx-over,.vtight mjx-stretchy-h{transform:translateY(.18em)!important}.math-box mjx-container,.math-box .MathJax{font-size:1.14em!important}.pagination{flex-wrap:wrap;justify-content:center;align-items:center;gap:12px 8px;margin-top:12px;padding:20px 6px;display:flex}.page-btn{background:var(--card);border:1px solid var(--border);font-family:var(--font);color:var(--text);cursor:pointer;white-space:nowrap;text-align:center;border-radius:10px;flex-shrink:0;min-width:36px;padding:8px 12px;font-size:1rem;font-weight:600;transition:all .15s}.page-btn:hover:not(:disabled){background:var(--accent);color:#000}.page-btn:disabled{opacity:.4;cursor:not-allowed}.page-info{color:var(--muted);white-space:nowrap;flex-shrink:0;font-size:.85rem}.page-jump{color:var(--muted);white-space:nowrap;flex-shrink:0;align-items:center;gap:6px;font-size:.85rem;display:flex}.page-jump-input{border:1px solid var(--border);background:var(--card);width:46px;color:var(--text);font-family:var(--font);text-align:center;border-radius:8px;outline:none;padding:6px;font-size:.85rem;font-weight:600;transition:border-color .15s}.page-jump-input:focus{border-color:var(--accent)}.q-statement{font-size:.89rem!important;line-height:1.7!important}.math-box{font-size:1.06rem!important;line-height:2!important}.step-text{font-size:.93rem!important;line-height:1.65!important}.step-label{font-size:.89rem!important;line-height:1.7!important;overflow:visible!important}@media (max-width:699px) and (orientation:portrait){.q-list{padding:0 10px}.q-statement{-webkit-overflow-scrolling:touch;padding-right:2px;overflow-x:auto}.q-statement mjx-container{max-width:none;display:inline-block}.q-statement:after{content:none}.q-statement.can-swipe:after{content:"Swipe →";letter-spacing:.2px;color:var(--muted);opacity:.85;margin-top:6px;font-size:.62rem;line-height:1;display:block}}@media (min-width:700px){.hero,.stats,.search-wrap,.filter-section,.section-head,.q-list,.empty,.topic-grid,.progress-wrap,.about-wrap{max-width:var(--content-max);margin-left:auto;margin-right:auto}.profile-menu{right:max(var(--content-pad-inline), calc((100vw - min(var(--content-max), 100vw)) / 2 + var(--content-pad-inline)))}.auth-inner{max-width:480px;margin-left:auto;margin-right:auto}.paywall-inner{max-width:520px;margin-left:auto;margin-right:auto}}a{color:inherit;text-decoration:none}.shell{width:min(960px,100% - 2rem);margin:0 auto;padding:1.5rem 0 3rem}.card{background:var(--card);border:1px solid var(--border);border-radius:16px}.shell form.card a{color:var(--accent);font-weight:600}button.billing-plan-btn{appearance:none;box-sizing:border-box;width:100%;font-family:var(--font);color:var(--text);background:var(--card);border:1px solid var(--border);cursor:pointer;text-align:center;border-radius:16px;margin:0;padding:.75rem 1rem;font-size:.9rem;font-weight:600;transition:border-color .15s,box-shadow .15s,background .15s;display:block}button.billing-plan-btn:hover:not(:disabled){background:#ffffff0a;border-color:#00d4ff59}button.billing-plan-btn:disabled{opacity:.65;cursor:not-allowed}button.billing-plan-btn.billing-plan-btn--selected{border-color:var(--accent);background:#00d4ff1a;box-shadow:0 0 0 1px #00d4ff38}button.billing-plan-btn.billing-plan-btn--spaced{margin-bottom:.6rem}a.billing-back-btn{box-sizing:border-box;font-family:var(--font);color:var(--accent);border:1px solid var(--border);background:#00d4ff12;border-radius:12px;align-items:center;gap:6px;margin-bottom:.75rem;padding:10px 14px;font-size:.82rem;font-weight:600;transition:border-color .15s,background .15s;display:inline-flex}a.billing-back-btn:hover{background:#00d4ff1f;border-color:#00d4ff59}