:root{--ink:#173b3b;--ink-soft:#4e696b;--dark:#0e4343;--teal:#137f76;--teal2:#1fa28e;--mint:#eaf9f2;--mint2:#d5f1e6;--blue:#e9f1ff;--yellow:#fff1c9;--lilac:#f3edff;--surface:#fff;--background:#fbfdfc;--border:#e0ebe7;--shadow:0 22px 55px rgba(27,78,73,.09);--radius:22px}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;color:var(--ink);font-family:system-ui,-apple-system,"Segoe UI",Roboto,Arial,sans-serif;background:var(--background);line-height:1.62;font-size:16px}button,textarea{font:inherit}button,a{-webkit-tap-highlight-color:transparent}a{color:inherit;text-decoration:none}a:focus-visible,button:focus-visible,textarea:focus-visible{outline:3px solid #e7a52e;outline-offset:3px}button{cursor:pointer}.skip-link{position:absolute;z-index:1000;top:-100px;left:10px;background:#fff;padding:10px}.skip-link:focus{top:10px}.container{width:min(1180px,calc(100% - 44px));margin:0 auto}.site-header{position:sticky;top:0;background:rgba(255,255,255,.96);backdrop-filter:blur(14px);z-index:100;box-shadow:0 1px 0 rgba(24,69,65,.08)}.header-inner{min-height:82px;display:flex;align-items:center;justify-content:space-between;gap:20px}.brand{display:flex;align-items:center;gap:12px;flex-shrink:0}.brand-mark{width:43px;height:43px;border-radius:14px;background:var(--teal);display:grid;place-items:center;color:white;font-size:28px;font-weight:900;position:relative;transform:rotate(-6deg)}.brand-mark i{font-size:13px;color:#186b64;background:#ffdf86;border-radius:50%;font-style:normal;line-height:21px;text-align:center;width:21px;height:21px;position:absolute;right:-7px;top:-6px;transform:rotate(6deg)}.brand-title{font-size:16px;font-weight:750;letter-spacing:-.3px;line-height:1.1}.brand-title strong{color:#148e80}.brand-title small{display:block;font-size:9px;letter-spacing:2px;color:#647f7e;margin-top:6px}.site-nav{display:flex;align-items:center;gap:4px}.nav-link{padding:13px 15px;border-radius:11px;font-size:14px;font-weight:680;color:#45625f;transition:.2s}.nav-link:hover,.nav-link.active{background:#eaf8f2;color:#0a766d}.menu-toggle{display:none;border:1px solid var(--border);background:white;border-radius:12px;min-width:44px;min-height:44px;font-size:25px;color:var(--ink)}.view[hidden]{display:none!important}.hero-wrap{background:radial-gradient(circle at 70% 18%,#d8f3df 0,transparent 37%),linear-gradient(115deg,#effaf4 0%,#ebf9f2 55%,#e6f7f1 100%);position:relative;overflow:hidden}.hero-grid{min-height:585px;display:grid;grid-template-columns:1.09fr .91fr;gap:45px;align-items:center;padding:74px 0 80px}.hero-content{z-index:2}.eyebrow,.section-kicker{display:inline-flex;align-items:center;gap:9px;letter-spacing:2.1px;color:#0c8d7a;font-size:11px;font-weight:900}.pulse-dot{display:inline-block;width:10px;height:10px;border-radius:50%;background:#28bf99;box-shadow:0 0 0 5px #d1f6e7}.hero-content h1{font-size:clamp(35px,4.7vw,62px);line-height:1.14;letter-spacing:-2.4px;font-weight:850;margin:22px 0 20px;color:#183e3c}.hero-content h1 span{color:#159d86}.hero-content>p{font-size:17px;color:#4f6c66;max-width:540px;line-height:1.85;margin:0 0 26px}.hero-content>p strong{color:#23504b}.hero-actions,.inline-actions{display:flex;gap:12px;flex-wrap:wrap}.btn{display:inline-flex;gap:12px;align-items:center;justify-content:center;border:1px solid transparent;border-radius:13px;padding:12px 20px;min-height:48px;font-size:14px;font-weight:800;transition:.2s;white-space:normal;text-align:center}.btn-primary{background:#08776f;color:white;box-shadow:0 8px 15px rgba(10,114,103,.15)}.btn-primary:hover{background:#075e57;transform:translateY(-1px)}.btn-light{background:#fff;color:#276960;border-color:#d9e7e2}.btn-light:hover{border-color:#63ad9e;background:#f6fffa}.btn[disabled]{opacity:.4;cursor:not-allowed;transform:none}.hero-notes{margin-top:26px;display:flex;flex-wrap:wrap;gap:17px;color:#57746b;font-size:12px;font-weight:650}.hero-notes span::first-letter{color:#0d9683}.hero-visual{position:relative;min-height:410px;display:grid;place-items:center}.browser-mock{border:1px solid #e6ebe7;background:white;box-shadow:0 31px 60px rgba(31,75,67,.12);border-radius:21px;transform:rotate(-2deg);width:min(440px,100%);padding:0 25px 27px;position:relative;z-index:3}.mock-top{display:flex;justify-content:space-between;align-items:center;border-bottom:1px solid #ebefed;font-size:12px;color:#90a5a0;padding:20px 0}.mock-circles{letter-spacing:4px;font-size:10px;color:#f8bd93}.mock-question{margin:27px 0 15px;font-size:23px;line-height:1.4;font-weight:820;color:#1b4545}.mock-reply{background:#f7faf8;border-radius:12px;padding:16px;color:#587271;font-size:14px;line-height:1.7}.mock-verdict{display:flex;align-items:center;gap:14px;margin-top:19px;padding:15px;border-radius:14px;background:#e8f8ef;border:1px solid #b9edd5}.verdict-icon{width:39px;height:39px;border-radius:50%;background:#21a586;color:#fff;display:grid;place-items:center;font-size:23px;font-weight:900}.mock-verdict strong,.mock-verdict small{display:block}.mock-verdict strong{color:#106b57}.mock-verdict small{font-size:12px;color:#5b786e;margin-top:3px}.floating-note{position:absolute;z-index:5;background:white;border-radius:13px;box-shadow:0 11px 35px #123f3320;padding:14px 17px;font-size:14px;color:#195c52}.note-a{top:22px;right:-12px;transform:rotate(7deg)}.note-b{bottom:18px;left:-22px;transform:rotate(-7deg)}.visual-dots{position:absolute;width:100px;height:100px;border-radius:50%}.dots-one{background:#ffdda2;top:26px;left:4px}.dots-two{background:#b6e8c6;right:-8px;bottom:20px;width:135px;height:135px}.wave-bottom{height:13px;position:absolute;bottom:0;left:0;width:100%;background:linear-gradient(90deg,#84cbb6 0 22%,#e9c470 22% 36%,#84cbb6 36% 55%,#c9e6d5 55% 100%);opacity:.5}.section-pad{padding-top:88px;padding-bottom:85px}.section-pad.compact{padding-top:75px}.section-heading{text-align:center;max-width:730px;margin:0 auto 34px}.section-heading.left{text-align:left;margin:0 0 26px}.section-heading h2,.journey-panel h2{font-size:clamp(28px,3vw,38px);line-height:1.25;letter-spacing:-1.1px;margin:13px 0 12px}.section-heading p,.journey-panel p{color:#617b76;font-size:15px;line-height:1.8;margin:0}.feature-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:17px}.feature-card{display:flex;flex-direction:column;align-items:flex-start;min-height:285px;padding:28px 24px;background:white;border:1px solid var(--border);border-radius:20px;box-shadow:0 4px 25px #226e5f08;transition:.2s}.feature-card:hover{border-color:#8ac8b5;box-shadow:var(--shadow);transform:translateY(-3px)}.feature-icon{font-size:29px;width:59px;height:59px;display:grid;place-items:center;border-radius:18px;margin-bottom:21px}.mint{background:#e1f6e9}.blue{background:#e8f2ff}.yellow{background:#fff2cd}.lilac{background:#f1edff}.feature-number{font-size:10px;letter-spacing:1.4px;color:#2b9c87;font-weight:900}.feature-card h3{font-size:19px;margin:8px 0 8px;letter-spacing:-.5px;line-height:1.28}.feature-card p{font-size:13px;color:#67817a;line-height:1.75;margin:0 0 18px}.feature-arrow{margin-top:auto;color:#108775;font-size:13px;font-weight:850}.journey-panel{background:#e4f4ea;border:1px solid #d3e8dc;border-radius:26px;padding:40px 65px;display:grid;grid-template-columns:1.3fr .7fr;align-items:center;min-height:320px;overflow:hidden}.journey-panel p{max-width:620px;margin-bottom:21px}.inline-link{font-weight:800;color:#127d6f}.inline-link:hover{text-decoration:underline}.journey-art{height:240px;display:grid;place-items:center;position:relative}.big-check{background:#fff;color:#1a967d;border-radius:50%;display:grid;place-items:center;width:170px;height:170px;font-size:110px;line-height:1;box-shadow:0 19px 40px #126e4b16;transform:rotate(-10deg)}.orbit{position:absolute;font-weight:800;border-radius:50%;display:grid;place-items:center;box-shadow:0 8px 22px #234a4018}.orbit-one{top:4px;right:30px;background:#ffd98b;width:59px;height:59px;font-size:29px}.orbit-two{bottom:0;right:48px;background:#abdbd0;width:47px;height:47px;font-size:23px}.orbit-three{left:12px;bottom:28px;background:#d8d4ff;width:51px;height:51px;font-size:27px}.mini-steps{display:grid;grid-template-columns:repeat(3,1fr);gap:22px}.mini-steps>div{padding:23px 27px;border:1px solid var(--border);border-radius:18px;background:white}.mini-steps span{display:inline-grid;place-items:center;width:33px;height:33px;border-radius:11px;background:#dcf7e8;color:#0a8b70;font-weight:900;margin-right:10px}.mini-steps strong{font-size:16px}.mini-steps p{color:#6b807c;font-size:13px;margin:12px 0 0 44px}.site-footer{background:#123f3c;color:#e9fbf5;margin-top:40px;padding:38px 0 0}.footer-inner{display:flex;justify-content:space-between;gap:20px;align-items:start;padding-bottom:32px}.footer-brand{font-weight:900;letter-spacing:.4px;font-size:20px}.footer-brand strong{color:#a6e9c2}.site-footer p{font-size:13px;color:#bdd9d2;margin:5px 0}.footer-links{display:flex;flex-wrap:wrap;gap:18px;font-size:13px;font-weight:700}.footer-links a:hover{text-decoration:underline}.footer-bottom{border-top:1px solid #ffffff25;padding:18px 0;font-size:12px;color:#b7d0c9}.page-hero{padding:65px 0 59px;background:linear-gradient(120deg,#ebf8ef,#eff8f5);border-bottom:1px solid #dcefe7}.page-hero-book{background:radial-gradient(circle at 90% 10%,#ffebbd,transparent 35%),linear-gradient(120deg,#e9f7ef,#f6fbf2)}.page-hero-steps{background:radial-gradient(circle at 90% 10%,#ccefff,transparent 35%),linear-gradient(120deg,#eef9f4,#e9f4ff)}.page-hero-practice{background:radial-gradient(circle at 88% 9%,#f9e5c5,transparent 34%),linear-gradient(120deg,#edf8f3,#f8f9f3)}.page-hero h1{font-size:clamp(32px,4vw,51px);line-height:1.2;letter-spacing:-1.4px;margin:14px 0 12px}.page-hero p{margin:0;max-width:715px;color:#597671;font-size:16px}.emoji{font-size:.8em}.page-hero-pills{margin-top:22px;display:flex;flex-wrap:wrap;gap:8px}.page-hero-pills span,.notice-pill{border-radius:100px;padding:6px 13px;background:#ffffffae;border:1px solid #dbeddf;color:#2f7263;font-size:12px;font-weight:750}.notice-pill{display:inline-flex;margin-top:23px}.book-area{padding:40px 0 70px}.book-layout{display:grid;grid-template-columns:258px minmax(0,1fr);gap:26px;align-items:start}.book-sidebar{background:white;border:1px solid var(--border);border-radius:17px;padding:20px 12px;position:sticky;top:100px}.sidebar-heading{font-size:11px;color:#73918b;letter-spacing:1.4px;font-weight:900;padding:5px 12px 12px}.book-index{display:flex;flex-direction:column;gap:3px}.book-index-btn{display:flex;text-align:left;gap:10px;width:100%;padding:10px 11px;border-radius:10px;background:transparent;border:0;color:#5e7570;font-size:12px;font-weight:650;line-height:1.5;align-items:center}.book-index-btn span{font-size:10px;flex-shrink:0;color:#87a099}.book-index-btn:hover,.book-index-btn.active{background:#eaf7f0;color:#08776e}.book-index-btn.active span{color:#0b8a71}.book-main{min-width:0}.book-toolbar{display:flex;align-items:center;justify-content:space-between;color:#5d7972;font-size:13px;font-weight:800;margin:8px 0 13px}.book-tag{color:#14977f;font-size:10px;letter-spacing:1px}.book-progress,.exercise-progress{width:100%;height:7px;border-radius:100px;background:#e4efeb;overflow:hidden}.book-progress div,.exercise-progress div{height:100%;border-radius:100px;background:linear-gradient(90deg,#2ccba4,#098679);transition:width .2s ease}.book-paper{margin:16px 0 22px;min-height:540px;border:1px solid #e3e9e4;border-radius:19px;background:white;box-shadow:var(--shadow);padding:48px 62px;position:relative;overflow:hidden}.book-paper:before{content:'';position:absolute;top:0;left:0;right:0;height:9px;background:linear-gradient(90deg,#42b49b 0%,#8bdfc0 55%,#f5d28a 55%,#f5d28a 100%)}.book-pg-label{color:#119583;font-size:11px;letter-spacing:1.7px;font-weight:900}.book-paper h2{font-size:clamp(26px,3.6vw,37px);line-height:1.25;margin:16px 0 24px;letter-spacing:-.9px}.book-paper p{font-size:15.5px;color:#405f5a;line-height:1.85;margin:0 0 16px}.book-paper h3{font-size:19px;margin:20px 0 8px;color:#176b60}.book-paper ul,.book-paper ol{margin:5px 0 20px;padding-left:25px;color:#45615c;line-height:1.85;font-size:15px}.book-paper li+li{margin-top:8px}.book-highlight{padding:19px 21px;margin:24px 0;border-radius:15px;border-left:4px solid #18a58e;background:#eaf9f0;color:#235b51;line-height:1.8}.book-highlight strong{color:#0d7364}.book-warning{border-left-color:#eeb74e;background:#fff5d9}.book-example{background:#f6f9fa;border-radius:14px;padding:18px 20px;margin:22px 0;border:1px solid #e4edf0}.book-example .small-overline,.small-overline{display:block;font-size:10px;font-weight:900;letter-spacing:1.3px;color:#8a9f9b}.book-example p{font-size:16px;font-weight:750;margin:9px 0}.book-cover{background:radial-gradient(circle at 90% 15%,#b8eee0,transparent 35%),linear-gradient(140deg,#effaf3,#fff8e6);border-radius:17px;min-height:430px;display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center;padding:38px 30px}.book-cover .cover-icon{width:116px;height:116px;display:grid;place-items:center;border-radius:35px;background:#fff;box-shadow:0 15px 29px #11725d16;font-size:67px;transform:rotate(-6deg)}.book-cover h2{font-size:clamp(35px,5vw,59px);max-width:600px;color:#117967;margin:26px 0 13px}.book-cover p{font-size:19px;max-width:440px}.book-cover small{font-size:12px;letter-spacing:2px;color:#4b8e7d;font-weight:900;margin-top:30px}.book-controls{display:flex;justify-content:space-between;align-items:center;gap:12px}.book-controls>span{font-size:12px;color:#7a948a;font-weight:800}.steps-container{padding-top:48px}.steps-row{display:grid;grid-template-columns:repeat(3,1fr);gap:20px;margin-bottom:44px}.step-tile{background:white;border:1px solid var(--border);border-radius:20px;padding:30px 28px}.step-index{font-size:11px;letter-spacing:1.2px;font-weight:900;color:#128872}.step-visual{display:block;font-size:45px;margin:18px 0 12px}.step-tile h2{font-size:25px;letter-spacing:-.5px;margin:0 0 9px}.step-tile p{margin:0;color:#667e78;line-height:1.8;font-size:14px}.practice-panel{border-radius:24px;background:#fff;border:1px solid var(--border);padding:39px}.check-work{display:grid;grid-template-columns:.8fr 1.2fr;gap:30px}.example-quote{background:linear-gradient(150deg,#e3f6ed,#dff1ff);border-radius:18px;padding:28px;align-self:start}.example-quote p{font-weight:750;font-size:21px;line-height:1.5;margin:15px 0}.example-quote small{font-size:13px;color:#42716b}.worksheet{display:flex;flex-direction:column;gap:9px}.worksheet label{font-weight:750;font-size:13px;margin-top:5px}.worksheet textarea{border:1px solid #d6e5e0;border-radius:12px;width:100%;padding:13px 15px;resize:vertical;min-height:75px;color:#234944;background:#fbfefd}.worksheet textarea::placeholder{color:#95a7a0}.inline-actions{margin-top:9px}.answer-box{background:#ecf8ee;border:1px solid #bdebd2;border-radius:13px;padding:18px;margin:10px 0}.answer-box p{margin:8px 0 6px}.answer-box small{font-size:12px;color:#627a70}.tip-strip{background:#eaf7f1;display:flex;gap:20px;align-items:center;margin-top:28px;padding:21px 24px;border-radius:17px;color:#40635d}.tip-strip span{font-size:32px}.tip-strip p{margin:0;font-size:14px}.mode-tabs{display:inline-flex;gap:9px;margin-bottom:23px;flex-wrap:wrap}.mode-tab{border:1px solid #d9e9e3;background:white;color:#638077;border-radius:13px;padding:14px 21px;font-size:14px;font-weight:800;min-height:48px}.mode-tab:hover{color:#0c796c}.mode-tab.active{background:#0b776d;color:white;border-color:#0b776d}.exercise-shell{background:white;border:1px solid var(--border);border-radius:23px;padding:38px 45px;box-shadow:var(--shadow);max-width:850px;margin:0 auto}.exercise-top{display:flex;justify-content:space-between;align-items:center;font-size:12px;letter-spacing:.6px;color:#6a877c;font-weight:900;margin-bottom:13px}.exercise-question{font-size:clamp(21px,3.3vw,28px);font-weight:850;line-height:1.5;margin:33px 0 25px;letter-spacing:-.3px}.choice-list{display:grid;gap:12px}.choice-btn{width:100%;border:1px solid #dce9e3;border-radius:14px;background:#fbfefd;text-align:left;color:#244b46;padding:15px 18px;min-height:60px;font-size:15px;font-weight:650;display:flex;gap:14px;align-items:center;transition:background .2s,border-color .2s}.choice-btn:hover:not(:disabled){background:#eefaf4;border-color:#a0d9bf}.choice-btn .choice-symbol{background:#e9f4ed;border:1px solid #d5e9de;border-radius:9px;display:grid;place-items:center;min-width:31px;min-height:31px;font-weight:900;color:#53736b}.choice-btn.correct{background:#e4f8e9;border-color:#36ae79;color:#116a4f}.choice-btn.correct .choice-symbol{background:#1ca57d;color:white;border-color:#1ca57d}.choice-btn.wrong{background:#fff1ee;border-color:#dc8b7b;color:#a34236}.choice-btn.wrong .choice-symbol{background:#d86857;color:white;border-color:#d86857}.choice-btn:disabled{cursor:default}.feedback-box{margin-top:20px;background:#ecfaf2;border:1px solid #c1e9cf;border-radius:14px;padding:20px;color:#385b52}.feedback-box.fail{background:#fff7e8;border-color:#efdaa8}.feedback-box strong{display:block;font-size:16px;margin-bottom:5px}.feedback-box p{margin:0;line-height:1.75;font-size:14px}.exercise-bottom{margin-top:24px;display:flex;gap:12px;align-items:center;justify-content:space-between;flex-wrap:wrap}.exercise-bottom .btn-primary{margin-left:auto}.result-screen{text-align:center;padding:35px 10px}.result-emoji{font-size:70px}.result-screen h2{font-size:32px;margin:10px 0}.result-screen .result-score{font-size:48px;color:#098776;font-weight:900;line-height:1.3}.result-screen p{max-width:510px;color:#637e74;margin:12px auto 0}.privacy-note{margin:26px auto 0;max-width:850px;display:flex;gap:14px;align-items:start;color:#5d7770;font-size:13px;padding:14px 4px}.privacy-note span{font-size:22px}.privacy-note p{margin:0}.page-hero h1 .emoji{display:inline-block;vertical-align:middle}.site-footer{margin-top:30px}
@media(max-width:1050px){.feature-grid{grid-template-columns:repeat(2,1fr)}.hero-grid{gap:15px}.floating-note{font-size:12px}.note-b{left:-5px}.note-a{right:0}.book-layout{grid-template-columns:225px minmax(0,1fr)}.book-paper{padding:34px 38px}}
@media(max-width:760px){.container{width:min(100% - 30px,1180px)}.header-inner{min-height:69px}.brand-mark{width:39px;height:39px}.brand-title{font-size:14px}.brand-title small{font-size:8px;letter-spacing:1.3px}.menu-toggle{display:block}.site-nav{display:none;position:absolute;top:69px;left:0;right:0;background:white;box-shadow:0 10px 25px #0a4c3c12;padding:12px 15px 17px;border-top:1px solid #e8f0e9;flex-direction:column;align-items:stretch}.site-nav.open{display:flex}.nav-link{font-size:15px;padding:13px}.hero-grid{grid-template-columns:1fr;min-height:0;padding:52px 0 43px}.hero-content h1{letter-spacing:-1.3px;font-size:clamp(34px,8vw,48px)}.hero-content>p{font-size:15px}.hero-visual{min-height:345px}.browser-mock{width:min(390px,87%)}.mock-question{font-size:21px}.note-a{top:4px}.note-b{bottom:6px;left:0}.section-pad{padding:58px 0}.section-heading h2{font-size:29px}.journey-panel{grid-template-columns:1fr;padding:33px 30px}.journey-art{height:170px}.big-check{width:130px;height:130px;font-size:86px}.orbit-one{right:30%}.mini-steps{grid-template-columns:1fr}.book-layout{grid-template-columns:1fr}.book-sidebar{position:static;padding:15px}.book-index{display:flex;flex-direction:row;overflow-x:auto;padding:2px 0 5px;gap:6px;scrollbar-width:thin}.book-index-btn{flex:0 0 163px;min-height:60px}.steps-row{grid-template-columns:1fr;gap:13px}.step-tile{padding:23px}.step-visual{margin:9px 0;font-size:38px}.check-work{grid-template-columns:1fr}.practice-panel{padding:24px}.exercise-shell{padding:25px}.page-hero{padding:47px 0}.footer-inner{flex-direction:column}.footer-links{gap:11px}.site-footer{margin-top:20px}}
@media(max-width:520px){.feature-grid{grid-template-columns:1fr}.feature-card{min-height:0;padding:23px}.hero-actions{align-items:stretch}.hero-actions>.btn{width:100%}.hero-notes{gap:8px 12px}.browser-mock{padding:0 15px 18px}.mock-question{font-size:18px}.mock-reply{font-size:13px}.mock-verdict{padding:11px}.floating-note{padding:9px 11px;font-size:10px}.section-heading h2{font-size:27px}.journey-panel{padding:29px 22px}.book-paper{min-height:440px;padding:27px 22px}.book-paper h2{font-size:28px}.book-paper p,.book-paper li{font-size:14px}.book-controls .btn{padding:11px;min-height:45px;font-size:12px}.book-controls>span{font-size:10px}.mode-tabs{display:grid;grid-template-columns:1fr 1fr;width:100%}.mode-tab{padding:10px 6px;font-size:12px}.exercise-shell{padding:19px 17px}.choice-btn{font-size:14px;padding:13px}.exercise-bottom .btn{font-size:12px;padding:10px}.page-hero h1{font-size:33px}.page-hero p{font-size:14px}}
@media(prefers-reduced-motion:reduce){*,*:before,*:after{scroll-behavior:auto!important;transition:none!important}}
/* Giữ sách số gọn trong màn hình điện thoại; mục lục cuộn ngang độc lập. */
.book-layout,.book-sidebar,.book-main{min-width:0;max-width:100%}
.book-index{max-width:100%}
@media(max-width:760px){.book-layout{grid-template-columns:minmax(0,1fr)}.book-index{width:100%;overflow-x:auto}}