:root{--color-text: #1C1917;--color-text-secondary: #44403c;--color-text-muted: #78716c;--color-text-ghost: #a8a29e;--color-bg: #FAF9F5;--color-border: rgba(28, 25, 23, .08);--color-border-strong: rgba(28, 25, 23, .12);--color-accent: #2563eb;--content-width: 680px;--sidebar-width: 220px;--container-width: 1100px;--header-height: 56px;--transition-fast: .15s cubic-bezier(.4, 0, .2, 1);--transition-base: .25s cubic-bezier(.4, 0, .2, 1)}.lesson-page{max-width:var(--container-width);margin:0 auto;padding:0 2rem}.lesson-layout{display:grid;grid-template-columns:minmax(0,var(--content-width)) var(--sidebar-width);gap:4rem;align-items:start;padding-top:3.5rem;padding-bottom:2rem}.lesson-main{min-width:0}.lesson-title{font-size:clamp(2rem,5vw,2.75rem);font-weight:750;line-height:1.15;letter-spacing:-.03em;color:var(--color-text);margin:0 0 .625rem}.lesson-meta{display:flex;align-items:center;gap:.5rem;font-size:.9375rem;color:var(--color-text-muted);margin-bottom:2.75rem}.meta-item{font-weight:450}.meta-sep{color:var(--color-text-ghost);user-select:none}.breadcrumb{display:flex;align-items:center;gap:.5rem;font-size:.8125rem;color:var(--color-text-muted);margin-bottom:1.25rem}.breadcrumb svg{width:14px;height:14px;flex-shrink:0}.breadcrumb-link{color:var(--color-text-muted);text-decoration:none;transition:color var(--transition-fast)}.breadcrumb-link:hover{color:var(--color-text)}.breadcrumb-sep{color:var(--color-text-ghost);user-select:none}.lesson-content{font-size:1.0625rem;line-height:1.8;color:var(--color-text-secondary)}.lesson-content p{margin:0 0 1.5rem}.lesson-content>p:first-of-type{font-size:1.125rem;line-height:1.75;color:var(--color-text)}.lesson-content h2{font-size:1.625rem;font-weight:700;line-height:1.3;letter-spacing:-.02em;color:var(--color-text);margin:3rem 0 1rem;scroll-margin-top:calc(var(--header-height) + 1.5rem)}.lesson-content h2:first-child{margin-top:0}.lesson-content h3{font-size:1.1875rem;font-weight:600;line-height:1.4;letter-spacing:-.01em;color:var(--color-text);margin:2.25rem 0 .625rem;scroll-margin-top:calc(var(--header-height) + 1.5rem)}.lesson-content h4{font-size:1rem;font-weight:600;line-height:1.5;color:var(--color-text);margin:1.75rem 0 .5rem;scroll-margin-top:calc(var(--header-height) + 1.5rem)}.lesson-content strong{font-weight:600;color:var(--color-text)}.lesson-content em{font-style:italic}.lesson-content a{color:var(--color-accent);text-decoration:underline;text-decoration-color:#2563eb59;text-underline-offset:2px;text-decoration-thickness:1px;transition:text-decoration-color var(--transition-fast)}.lesson-content a:hover{text-decoration-color:var(--color-accent)}.lesson-content ul,.lesson-content ol{margin:1.25rem 0 1.5rem;padding-left:0}.lesson-content ul{list-style:none}.lesson-content ul li{position:relative;margin-bottom:.625rem;padding-left:1.375rem;line-height:1.7}.lesson-content ul li:before{content:"";position:absolute;left:0;top:.625rem;width:5px;height:5px;background:var(--color-text-ghost);border-radius:50%}.lesson-content ol{list-style:none;counter-reset:ol-counter}.lesson-content ol li{position:relative;margin-bottom:.625rem;padding-left:1.75rem;line-height:1.7;counter-increment:ol-counter}.lesson-content ol li:before{content:counter(ol-counter) ".";position:absolute;left:0;color:var(--color-text-muted);font-weight:500;font-size:.9375rem}.lesson-content code{font-family:SF Mono,Fira Code,Consolas,monospace;font-size:.875em;padding:.125em .375em;background:#1c19170d;border-radius:4px;color:var(--color-text)}.lesson-content pre{margin:1.75rem 0;padding:1.25rem 1.5rem;background:#18181b;border-radius:10px;overflow-x:auto;-webkit-overflow-scrolling:touch}.lesson-content pre code{padding:0;background:transparent;font-size:.8125rem;line-height:1.7;color:#e4e4e7}.lesson-content blockquote{margin:1.75rem 0;padding:1rem 1.25rem;background:#1c191706;border-left:3px solid var(--color-text);border-radius:0 6px 6px 0}.lesson-content blockquote p{margin:0;color:var(--color-text);font-size:1rem}.lesson-content blockquote p:not(:last-child){margin-bottom:.75rem}.lesson-content img{display:block;margin:2rem 0;border-radius:8px;max-width:100%;height:auto}.article-video{margin:40px 0}.lesson-content hr{margin:2.5rem 0;border:0;height:1px;background:var(--color-border)}.lesson-toc{position:sticky;top:calc(var(--header-height) + 3.5rem);max-height:calc(100vh - var(--header-height) - 7rem);overflow-y:auto;scrollbar-width:none;-ms-overflow-style:none}.lesson-toc::-webkit-scrollbar{display:none}.toc-nav{padding-left:0}.toc-header{font-size:.75rem;font-weight:600;text-transform:uppercase;letter-spacing:.1em;color:var(--color-text-ghost);margin-bottom:.875rem}.toc-list{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:.25rem}.toc-list li{margin:0}.toc-link{display:block;font-size:.8125rem;line-height:1.5;color:var(--color-text-muted);text-decoration:none;padding:.1875rem 0;transition:color var(--transition-fast)}.toc-link:hover{color:var(--color-text)}.toc-link.is-active{color:var(--color-text);font-weight:550}.lesson-nav{display:flex;justify-content:space-between;align-items:center;gap:2rem;margin-top:4rem;padding-top:2rem;border-top:1px solid var(--color-border);margin-bottom:2rem}.nav-link{display:inline-flex;align-items:center;gap:.5rem;font-size:.9375rem;font-weight:500;color:var(--color-text-muted);text-decoration:none;transition:color var(--transition-fast)}.nav-link:hover{color:var(--color-text)}.nav-link--next{margin-left:auto}.nav-link__arrow{font-size:1rem;line-height:1;transition:transform var(--transition-fast)}.nav-link--prev:hover .nav-link__arrow{transform:translate(-2px)}.nav-link--next:hover .nav-link__arrow{transform:translate(2px)}.nav-link__text{max-width:260px;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}@media(max-width:1024px){.lesson-layout{grid-template-columns:1fr;gap:0}.lesson-toc{display:none}}@media(max-width:768px){.lesson-page{padding:0 1.5rem}.lesson-layout{padding-top:2rem}.lesson-title{font-size:1.875rem}.lesson-meta{font-size:.875rem;margin-bottom:2rem}.lesson-content{font-size:1rem}.lesson-content>p:first-of-type{font-size:1.0625rem}.lesson-content h2{font-size:1.375rem;margin-top:2.5rem}.lesson-content h3{font-size:1.0625rem;margin-top:2rem}.lesson-content pre{margin-left:-1.5rem;margin-right:-1.5rem;border-radius:0;padding:1rem 1.5rem}.lesson-nav{flex-direction:column;align-items:stretch;gap:.875rem;margin-top:3rem;padding-top:1.5rem}.nav-link{font-size:.875rem}.nav-link--next{margin-left:0;justify-content:flex-end}.nav-link__text{max-width:180px}}@media(max-width:480px){.lesson-page{padding:0 1rem}.lesson-layout{padding-top:1.5rem}.lesson-title{font-size:1.625rem}.lesson-content pre{margin-left:-1rem;margin-right:-1rem;padding:1rem}.lesson-content ul li,.lesson-content ol li{padding-left:1.25rem}.lesson-content ol li:before{font-size:.875rem}}.nav-link:focus-visible,.toc-link:focus-visible{outline:2px solid var(--color-accent);outline-offset:2px;border-radius:3px}.practice-section{margin:2rem 0;font-family:inherit}.ps-header{display:flex;align-items:flex-start;justify-content:space-between;gap:8px;margin-bottom:20px}.ps-header .ps-rules{margin-bottom:0;flex:1;min-width:0}.ps-mute-btn{flex-shrink:0;display:flex;align-items:center;justify-content:center;width:32px;height:32px;border:none;background:transparent;color:#c4bfb8;cursor:pointer;border-radius:6px;padding:0;transition:color .15s ease,background .15s ease;-webkit-tap-highlight-color:transparent}.ps-mute-btn:hover{color:#8a8680;background:#f5f3ef}.ps-mute-btn:focus-visible{outline:2px solid #1a1814;outline-offset:2px}.ps-mute-btn--muted{color:#1a1814}.ps-mute-icon{width:18px;height:18px;display:block}.ps-mute-icon--off,.ps-mute-btn--muted .ps-mute-icon--on{display:none}.ps-mute-btn--muted .ps-mute-icon--off{display:block}.ps-progress-track{width:100%;height:2px;background:#edeae4;border-radius:99px;overflow:hidden;margin-bottom:28px}.ps-progress-fill{height:100%;background:#1a1814;border-radius:99px;width:0%;transition:width .5s cubic-bezier(.34,1.2,.64,1)}.ps-rules{display:flex!important;gap:6px;flex-wrap:wrap;margin-bottom:20px;padding:14px 16px;background:#faf9f7;border:1px solid #edeae4;border-radius:12px;transition:background .4s ease,border-color .4s ease}.ps-rules--mastered{background:#f0faf4!important;border-color:#c2e8d2!important}.ps-rules--mastered:after{content:"You’ve mastered this topic!";display:block;width:100%;font-size:.8rem!important;font-weight:600!important;color:#2d6a4f;margin-top:6px;padding-top:10px;border-top:1px solid #c2e8d2}.ps-rule{display:flex!important;align-items:center;gap:8px;flex:1 1 100px;min-width:0}.ps-rule-icon{width:22px;height:22px;flex-shrink:0;color:#d4d0c8;transition:color .35s ease}.ps-rule--mastered .ps-rule-icon{color:#2d6a4f}.ps-rule-icon svg{width:22px;height:22px;display:block;overflow:visible}.ps-rule-arc{transition:stroke-dashoffset .45s cubic-bezier(.34,1.2,.64,1)}.ps-rule-info{display:flex;flex-direction:column;gap:1px;min-width:0}.ps-rule-label{font-size:.78rem!important;font-weight:600!important;color:#6a6560!important;line-height:1.2;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;transition:color .35s ease}.ps-rule--mastered .ps-rule-label{color:#2d6a4f!important}.ps-rule-count{font-size:.72rem!important;color:#b4b0a8!important;font-variant-numeric:tabular-nums;transition:color .35s ease}.ps-rule--mastered .ps-rule-count{color:#2d6a4f!important;font-weight:600!important}.ps-streak{display:inline-flex!important;align-items:center;gap:5px;background:#fff8ec;border:1px solid #fde8b0;border-radius:99px;padding:3px 10px;margin-bottom:18px;font-size:12px;font-weight:600;color:#b45309}.ps-streak-count{color:#b45309}.ps-streak-fire{font-size:14px;line-height:1}.ps-streak-label{color:#b45309;font-weight:400}@keyframes ps-streak-pop{0%{transform:scale(1)}45%{transform:scale(1.2)}to{transform:scale(1)}}.ps-streak--pop{animation:ps-streak-pop .28s cubic-bezier(.34,1.56,.64,1) both}.ps-q{background:#fff!important;border-radius:14px!important;padding:20px 22px 18px!important;box-shadow:0 1px 3px #0000000f,0 0 0 1px #0000000a!important;border:none!important;transition:box-shadow .2s ease,background .2s ease;margin-bottom:8px!important}.ps-q--single{animation:ps-q-in .2s ease both}@keyframes ps-q-in{0%{opacity:0;transform:translateY(5px)}to{opacity:1;transform:translateY(0)}}.ps-q.answered-correct{box-shadow:0 1px 3px #0000000a,0 0 0 1.5px #b3dfc6!important;background:#f7fcf9!important}.ps-q.answered-wrong{box-shadow:0 1px 3px #0000000a,0 0 0 1.5px #ecd5d5!important;background:snow!important}.ps-q-sentence{font-size:1.05rem!important;line-height:1.7!important;color:#1a1814!important;margin:0 0 16px!important}.ps-blank{display:inline-block;min-width:44px;border-bottom:2px solid #d4d0c8;margin:0 2px;vertical-align:baseline;text-align:center;font-weight:600;color:#1a1814;transition:border-color .2s ease,color .2s ease;position:relative;top:2px;padding:0 3px;text-decoration:none!important}.ps-blank:empty:after{content:"· · ·";color:#d4d0c8;font-weight:400;font-size:.85em;letter-spacing:1px}.ps-blank--filled{border-bottom-color:#1a1814}.ps-blank--correct{border-bottom-color:#2d6a4f!important;color:#2d6a4f!important}.ps-blank--wrong{border-bottom-color:#e8b4b4!important;color:#c0392b!important}@keyframes ps-pop{0%{transform:scale(.75) translateY(3px);opacity:0}65%{transform:scale(1.08) translateY(-1px);opacity:1}to{transform:scale(1) translateY(0)}}.ps-blank--pop{animation:ps-pop .22s cubic-bezier(.34,1.56,.64,1) both}.ps-mc-opts{display:flex!important;flex-wrap:wrap;gap:7px}.ps-mc-opt{display:inline-flex!important;align-items:center;padding:8px 18px!important;border:1.5px solid #e8e4dc!important;border-radius:99px!important;background:#fff!important;font-family:inherit!important;font-size:.875rem!important;font-weight:500!important;color:#4a4640!important;cursor:pointer!important;transition:border-color .15s ease,background .15s ease,color .15s ease;box-shadow:none!important;line-height:1.4;-webkit-tap-highlight-color:transparent;touch-action:manipulation;user-select:none}.ps-mc-opt:hover:not(:disabled){border-color:#1a1814!important;color:#1a1814!important;background:#fafaf8!important}.ps-mc-opt:active:not(:disabled){transform:scale(.97)}.ps-mc-opt.correct{border-color:#2d6a4f!important;background:#edf7f2!important;color:#2d6a4f!important;font-weight:600!important}.ps-mc-opt.wrong{border-color:#e8b4b4!important;background:#fdf3f3!important;color:#c0392b!important}.ps-mc-opt:disabled{cursor:default!important}.ps-fill-input{display:inline-block!important;padding:0 0 6px!important;border:none!important;border-bottom:2px solid #d4d0c8!important;border-radius:0!important;background:transparent!important;font-family:inherit!important;font-size:1rem!important;color:#1a1814!important;width:140px;max-width:calc(100% - 8px);outline:none!important;box-shadow:none!important;vertical-align:baseline;margin:0 4px;transition:border-color .15s ease;-webkit-appearance:none;appearance:none}.ps-fill-input::placeholder{color:#c4bfb8!important}.ps-fill-input:focus{border-bottom-color:#1a1814!important}.ps-fill-input.correct{border-bottom-color:#2d6a4f!important;color:#2d6a4f!important}.ps-fill-input.wrong{border-bottom-color:#e8b4b4!important;color:#c0392b!important}.ps-fill-input:disabled{cursor:default!important}.ps-fill-actions{display:flex!important;align-items:center;gap:10px;margin-top:16px;flex-wrap:wrap}.ps-check-btn{display:inline-flex!important;align-items:center;padding:9px 22px!important;background:#1a1814!important;color:#fff!important;border:none!important;border-radius:99px!important;font-family:inherit!important;font-size:.875rem!important;font-weight:500!important;cursor:pointer!important;letter-spacing:.01em;transition:background .15s ease,transform .1s ease;box-shadow:none!important;-webkit-tap-highlight-color:transparent;touch-action:manipulation;user-select:none;min-height:40px}.ps-check-btn:hover{background:#2d2a25!important}.ps-check-btn:active{transform:scale(.97)}.ps-skip-btn{display:inline-flex!important;align-items:center;padding:8px!important;background:transparent!important;color:#c4bfb8!important;border:none!important;font-family:inherit!important;font-size:.8rem!important;cursor:pointer!important;transition:color .15s ease;box-shadow:none!important;text-decoration:underline;text-underline-offset:3px;text-decoration-color:#dedad2;-webkit-tap-highlight-color:transparent;min-height:40px}.ps-skip-btn:hover{color:#8a8680!important}.ps-hint{display:none!important}.ps-hint.visible{display:block!important;margin-top:16px!important;padding:13px 16px!important;border-radius:10px!important;background:#fafaf8!important;border:1px solid #f0ede6!important;animation:ps-hint-in .18s ease both}@keyframes ps-hint-in{0%{opacity:0;transform:translateY(-3px)}to{opacity:1;transform:translateY(0)}}.ps-hint-wrong{display:flex!important;align-items:center;gap:8px;margin-bottom:5px}.ps-hint-correct{display:flex!important;align-items:center;gap:8px}.ps-hint-icon{width:15px!important;height:15px!important;border-radius:50%!important;font-size:8px!important;display:flex!important;align-items:center;justify-content:center;flex-shrink:0;line-height:1}.ps-hint-icon--x{background:#fdecea!important;color:#c0392b!important}.ps-hint-icon--check{background:#e4f3eb!important;color:#2d6a4f!important}.ps-hint-wrong .ps-hint-word{font-size:.875rem!important;color:#c0392b!important;text-decoration:line-through;text-decoration-color:#e8b4b4;word-break:break-word}.ps-hint-correct .ps-hint-word{font-size:.875rem!important;font-weight:600!important;color:#2d6a4f!important}.ps-hint-rule{font-size:.78rem!important;color:#9a9590!important;margin-top:9px!important;padding-top:9px!important;border-top:1px solid #eeebe4!important;line-height:1.55}.ps-source{margin-top:12px!important;margin-bottom:0!important;font-size:.75rem!important;color:#c4bfb8!important;font-style:italic;line-height:1.4}.ps-results{margin-top:20px;padding:20px 22px!important;border-radius:14px!important;border:1px solid #e8e4dc!important;background:#fafaf8!important}.ps-results--good{background:#f7fcf9!important;border-color:#d5eede!important}.ps-results--perfect{background:#f0faf4!important;border-color:#c2e8d2!important}.ps-results-head{display:flex;align-items:center;gap:12px;margin-bottom:14px}.ps-results-emoji{font-size:1.8rem;line-height:1;flex-shrink:0}.ps-results-title{display:flex;align-items:baseline;gap:8px}.ps-results-score{font-size:1.5rem!important;font-weight:700!important;color:#1a1814!important;line-height:1}.ps-results--good .ps-results-score,.ps-results--perfect .ps-results-score{color:#2d6a4f!important}.ps-results-pct{font-size:.9rem;font-weight:500;color:#b4b0a8}.ps-results--good .ps-results-pct,.ps-results--perfect .ps-results-pct{color:#68b08a}.ps-results-stats{display:flex;gap:6px;margin-bottom:14px}.ps-results-stat{display:flex;flex-direction:column;align-items:center;gap:2px;flex:1;padding:8px 6px;background:#00000008;border-radius:10px}.ps-results-stat-icon{font-size:.7rem;color:#b4b0a8;line-height:1}.ps-results-stat-val{font-size:1rem;font-weight:700;color:#1a1814;font-variant-numeric:tabular-nums;line-height:1.2}.ps-results-stat-lbl{font-size:.68rem;color:#b4b0a8;text-transform:uppercase;letter-spacing:.04em}.ps-results-msg{font-size:.85rem!important;color:#8a8680!important;margin:0 0 6px!important;line-height:1.5}.ps-results-prev{font-size:.75rem!important;color:#c4bfb8!important;margin:0!important;font-variant-numeric:tabular-nums}.ps-results-reset{margin-top:14px!important;padding-top:14px!important;border-top:1px solid #edeae4}.ps-reset-btn{display:inline-flex;align-items:center;padding:7px 16px;background:transparent;color:#8a8680;border:1.5px solid #e8e4dc;border-radius:99px;font-family:inherit;font-size:.8rem;font-weight:500;cursor:pointer;transition:border-color .15s ease,color .15s ease,background .15s ease;-webkit-tap-highlight-color:transparent}.ps-reset-btn:hover{border-color:#c0392b;color:#c0392b;background:#fdf3f3}.ps-reset-btn:focus-visible{outline:2px solid #1a1814;outline-offset:2px}.ps-actions{margin-top:14px;display:flex!important;gap:10px;flex-wrap:wrap}.ps-keep-going{padding:11px 28px!important;background:#1a1814!important;color:#fff!important;border:none!important;border-radius:99px!important;font-family:inherit!important;font-size:.875rem!important;font-weight:500!important;cursor:pointer!important;letter-spacing:.01em;transition:background .15s ease,transform .1s ease;box-shadow:none!important;-webkit-tap-highlight-color:transparent;touch-action:manipulation;user-select:none;min-height:44px}.ps-keep-going:hover{background:#2d2a25!important}.ps-keep-going:active{transform:scale(.98)}@keyframes ps-fill-shake{0%,to{transform:translate(0)}20%{transform:translate(-5px)}40%{transform:translate(5px)}60%{transform:translate(-4px)}80%{transform:translate(4px)}}.ps-fill-input--shake{animation:ps-fill-shake .35s ease both;border-bottom-color:#e8b4b4!important}@media(max-width:480px){.practice-section{padding-top:2rem}.ps-q{padding:16px!important;border-radius:12px!important}.ps-q-sentence{font-size:.975rem!important}.ps-rules{padding:12px!important;gap:10px}.ps-rule{flex:1 1 80px}.ps-mc-opt{padding:8px 14px!important;font-size:.85rem!important;min-height:44px}.ps-check-btn{padding:10px 20px!important;min-height:44px}.ps-keep-going{width:100%!important;justify-content:center;min-height:48px}.ps-fill-input{width:120px;font-size:.975rem!important}.ps-fill-actions{margin-top:14px;gap:8px}.ps-blank{min-width:36px}.ps-source{font-size:.72rem!important}.ps-results{padding:16px!important}}@media(max-width:360px){.ps-mc-opt{font-size:.8rem!important;padding:7px 10px!important}.ps-rule-label{font-size:.72rem!important}.ps-rule-count{font-size:.68rem!important}.ps-fill-input{width:100px}}@media(prefers-reduced-motion:reduce){.ps-progress-fill,.ps-rule-arc,.ps-q,.ps-hint.visible,.ps-blank,.ps-mc-opt,.ps-check-btn,.ps-keep-going,.ps-rule-icon,.ps-rule-label,.ps-rule-count{transition:none!important;animation:none!important}.ps-q--single,.ps-blank--pop{animation:none!important}.ps-rule-arc{transition:none!important}.ps-streak--pop,.ps-hint.visible,.ps-fill-input--shake{animation:none!important}}