:root{--ds-blue:#1769ff;--ds-blue2:#0b4fe5;--ds-ink:#0e172a;--ds-muted:#61708a;--ds-line:#dfe6f0;--ds-bg:#f6f8fc;--ds-card:#fff;--ds-green:#0b9b6f;--ds-radius:24px}*{box-sizing:border-box}html{scroll-behavior:smooth}body.direct-study-page{margin:0;color:var(--ds-ink);background:#fff;font-family:Manrope,Inter,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Arial,sans-serif;font-size:16px;line-height:1.55;-webkit-font-smoothing:antialiased}.direct-study-page button,.direct-study-page textarea,.direct-study-page input{font:inherit}.direct-study-page a{color:inherit;text-decoration:none}.ds-shell{width:min(1160px,calc(100% - 40px));margin:0 auto}.sos-logo{display:inline-flex;align-items:center;gap:9px}.sos-logo-mark{position:relative;display:inline-grid;width:38px;height:38px;place-items:center}.sos-logo-mark svg{width:38px;height:38px}.sos-logo-mark i{position:absolute;color:#fff;font-size:9px;font-style:normal;font-weight:900;letter-spacing:-.4px}.sos-logo-word{display:flex;align-items:baseline;gap:0;font-size:20px;letter-spacing:-.7px}.sos-logo-word b{font-weight:800}.sos-logo-word strong{color:var(--ds-blue);font-weight:900}.ds-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.94);backdrop-filter:blur(18px);border-bottom:1px solid rgba(223,230,240,.85)}.ds-header-row{height:70px;display:flex;align-items:center;gap:28px}.ds-logo{flex:none}.ds-nav{display:flex;align-items:center;justify-content:center;gap:21px;flex:1;font-size:13.5px;font-weight:700;color:#48566f;white-space:nowrap}.ds-nav a:hover{color:var(--ds-blue)}.ds-header-actions{display:flex;align-items:center;gap:12px}.ds-login{font-size:14px;font-weight:800}.ds-button{display:inline-flex;align-items:center;justify-content:center;gap:8px;border:0;border-radius:14px;background:var(--ds-blue);color:#fff!important;min-height:48px;padding:0 22px;font-weight:850;cursor:pointer;box-shadow:0 9px 24px rgba(23,105,255,.18);transition:transform .16s ease,background .16s ease,box-shadow .16s ease}.ds-button:hover{background:var(--ds-blue2);transform:translateY(-1px);box-shadow:0 12px 30px rgba(23,105,255,.22)}.ds-button-small{min-height:42px;padding:0 16px;font-size:13px}.ds-menu-button{display:none;border:0;background:transparent;width:42px;height:42px;padding:10px}.ds-menu-button span{display:block;height:2px;background:#172238;margin:5px 0;border-radius:2px}.ds-mobile-menu{background:#fff;border-top:1px solid var(--ds-line);padding:14px 20px 22px}.ds-mobile-menu>a{display:block;padding:11px 0;font-weight:800}.ds-mobile-menu>div{display:flex;gap:10px;align-items:center;padding-top:10px}.ds-mobile-menu>div>a:first-child{font-weight:800;padding:12px}.ds-hero{padding:58px 0 72px;background:radial-gradient(circle at 15% 10%,rgba(23,105,255,.12),transparent 35%),linear-gradient(180deg,#f8fbff 0,#fff 100%);overflow:hidden}.ds-hero-grid{display:grid;grid-template-columns:minmax(0,.92fr) minmax(0,1.08fr);gap:52px;align-items:center}.ds-badge,.ds-kicker{display:inline-flex;align-items:center;gap:8px;color:var(--ds-blue);font-size:12px;font-weight:900;letter-spacing:.1em}.ds-badge i{width:8px;height:8px;border-radius:50%;background:#24c487;box-shadow:0 0 0 5px rgba(36,196,135,.12)}.ds-hero h1{font-size:clamp(40px,5vw,66px);line-height:1.02;letter-spacing:-.045em;margin:18px 0 20px;max-width:650px}.ds-lead{font-size:20px;line-height:1.55;color:#4e5f78;margin:0;max-width:620px}.ds-proof-row{display:flex;flex-wrap:wrap;gap:10px;margin-top:28px}.ds-proof-row span{background:#fff;border:1px solid #e5ebf4;border-radius:999px;padding:9px 12px;font-size:13px;font-weight:750;color:#3f4e66;box-shadow:0 4px 14px rgba(30,51,83,.05)}.ds-solver-card{background:#fff;border:1px solid #e2e8f2;border-radius:28px;box-shadow:0 28px 70px rgba(30,62,120,.14);padding:18px}.ds-solver-top{display:flex;justify-content:space-between;gap:12px;align-items:center;padding:2px 4px 14px}.ds-solver-top b{font-size:15px}.ds-solver-top span{font-size:11px;font-weight:850;color:var(--ds-blue);background:#edf4ff;border-radius:999px;padding:7px 9px}.ds-ai-form textarea{width:100%;resize:vertical;min-height:136px;border:1px solid #d9e1ed;border-radius:18px;padding:16px 17px;color:#172238;outline:none;background:#fbfcfe;line-height:1.55}.ds-ai-form textarea:focus{border-color:#8ab4ff;box-shadow:0 0 0 4px rgba(23,105,255,.09);background:#fff}.ds-attachments{display:flex;align-items:center;gap:9px;min-height:49px;padding:8px 1px}.ds-attach{display:inline-flex;align-items:center;gap:7px;border:1px solid #dfe6ef;border-radius:11px;padding:8px 10px;font-size:13px;font-weight:800;color:#3c4b62;background:#fff;cursor:pointer}.ds-attach:hover{border-color:#9abcf9}.ds-file-name{font-size:12px;color:var(--ds-muted);overflow:hidden;text-overflow:ellipsis;white-space:nowrap;min-width:0}.ds-submit{width:100%;border-radius:16px;min-height:52px}.ds-form-note{text-align:center;color:#738097;font-size:11.5px;padding:10px 2px 1px}.ds-answer{margin-top:14px;border:1px solid #dce5f1;border-radius:18px;background:#fbfdff;padding:18px;max-height:520px;overflow:auto;color:#1d2940}.ds-answer h2,.ds-answer h3{letter-spacing:-.02em}.ds-answer img{max-width:100%;height:auto;border-radius:14px}.ds-answer table{display:block;overflow:auto;border-collapse:collapse}.ds-answer td,.ds-answer th{border:1px solid #dfe6ef;padding:8px}.ds-thinking{display:flex;align-items:center;gap:10px;color:#516078;font-weight:750}.ds-spinner{width:18px;height:18px;border:2px solid #d7e4fb;border-top-color:var(--ds-blue);border-radius:50%;animation:ds-spin .8s linear infinite}@keyframes ds-spin{to{transform:rotate(360deg)}}.ds-answer-tools{display:flex;gap:9px;flex-wrap:wrap;margin-top:14px}.ds-answer-tools button,.ds-answer-tools a{border:1px solid #dce4ee;background:#fff;color:#26354e;border-radius:10px;padding:9px 12px;font-weight:800;font-size:12px;cursor:pointer}.ds-followup{display:grid;grid-template-columns:minmax(0,1fr) auto;gap:8px;margin-top:12px}.ds-followup input{min-width:0;border:1px solid #dce4ee;border-radius:11px;padding:10px 12px}.ds-section{padding:82px 0}.ds-section:nth-of-type(even){background:var(--ds-bg)}.ds-photo{background:#f3f7ff!important}.ds-photo-grid{display:grid;grid-template-columns:1fr .8fr;gap:60px;align-items:center}.ds-section h2{font-size:clamp(32px,4vw,48px);line-height:1.08;letter-spacing:-.038em;margin:12px 0 16px}.ds-section p{color:#5b6a81}.ds-photo ul,.ds-pro ul{padding:0;margin:24px 0 0;list-style:none;display:grid;gap:9px}.ds-photo li,.ds-pro li{position:relative;padding-left:25px;color:#394861}.ds-photo li:before,.ds-pro li:before{content:"✓";position:absolute;left:0;color:var(--ds-green);font-weight:900}.ds-dropzone{min-height:270px;border:2px dashed #a9c5f8;background:#fff;border-radius:26px;padding:30px;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:8px;color:#24334c;cursor:pointer}.ds-dropzone:hover{border-color:var(--ds-blue);background:#fbfdff}.ds-camera{display:grid;place-items:center;width:64px;height:64px;border-radius:19px;background:#eaf2ff;font-size:29px;margin-bottom:7px}.ds-dropzone b{font-size:18px}.ds-dropzone small{color:#718096}.ds-center-head{text-align:center;max-width:760px;margin:0 auto 38px}.ds-center-head p{font-size:17px;margin:0}.ds-feature-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:16px}.ds-feature-grid article,.ds-scenario-grid article,.ds-exam-grid article,.ds-steps article{background:#fff;border:1px solid var(--ds-line);border-radius:20px;padding:22px}.ds-feature-grid article>span{display:grid;place-items:center;width:38px;height:38px;border-radius:12px;background:#edf4ff;color:var(--ds-blue);font-weight:900}.ds-feature-grid h3,.ds-scenario-grid h3,.ds-exam-grid h3,.ds-steps h3{font-size:18px;letter-spacing:-.02em;margin:16px 0 8px}.ds-feature-grid p,.ds-scenario-grid p,.ds-exam-grid p,.ds-steps p{margin:0;font-size:14px}.ds-tutor{background:#0e1b33!important;color:#fff}.ds-tutor-grid{display:grid;grid-template-columns:.82fr 1.18fr;gap:54px;align-items:center}.ds-tutor .ds-kicker{color:#8cb6ff}.ds-tutor h2{color:#fff}.ds-tutor-copy p{color:#c0cee1;font-size:17px;max-width:520px;margin:0 0 24px}.ds-subject-mini{display:grid;grid-template-columns:1fr 1fr;gap:11px}.ds-subject-mini button{position:relative;text-align:left;background:#172741;color:#fff;border:1px solid #2a3c5a;border-radius:16px;padding:15px 42px 15px 16px;cursor:pointer;min-width:0}.ds-subject-mini button:hover{background:#1d3151;border-color:#4772b7}.ds-subject-mini b,.ds-subject-mini small{display:block}.ds-subject-mini small{margin-top:3px;color:#9fb0c8;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.ds-subject-mini span{position:absolute;right:15px;top:50%;transform:translateY(-50%);color:#8cb6ff}.ds-scenario-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:15px}.ds-scenario-grid button{border:0;background:transparent;padding:14px 0 0;color:var(--ds-blue);font-weight:850;cursor:pointer}.ds-exams{background:#f8f9fd!important}.ds-exam-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px;max-width:880px;margin:auto}.ds-exam-grid article>span{font-weight:900;color:var(--ds-blue);font-size:13px}.ds-button-outline{background:#fff;color:var(--ds-blue)!important;border:1px solid #adc7f7;box-shadow:none;margin-top:18px}.ds-button-outline:hover{background:#f1f6ff}.ds-check{background:#fff!important}.ds-check-grid{display:grid;grid-template-columns:1fr 1fr;gap:52px;align-items:center}.ds-check-form{border:1px solid var(--ds-line);border-radius:22px;padding:15px;background:#fbfcfe}.ds-check-form .ds-attach{margin:9px 0}.ds-answer-secondary{max-width:900px;margin:18px auto 0}.ds-steps{display:grid;grid-template-columns:repeat(3,1fr);gap:18px;max-width:900px;margin:auto}.ds-steps article{text-align:center}.ds-steps article>b{display:grid;place-items:center;width:42px;height:42px;border-radius:50%;background:var(--ds-blue);color:#fff;margin:0 auto}.ds-demo{background:#0f1c34!important;color:#fff}.ds-demo-grid{display:grid;grid-template-columns:.7fr 1.3fr;gap:56px;align-items:center}.ds-demo h2{color:#fff}.ds-demo p{color:#becce0}.ds-chat-demo{background:#fff;color:#19263d;border-radius:26px;padding:22px;box-shadow:0 30px 70px rgba(0,0,0,.18)}.ds-demo-user,.ds-demo-ai{max-width:86%;border-radius:18px;padding:13px 15px;margin:10px 0}.ds-demo-user{margin-left:auto;background:#edf4ff}.ds-demo-ai{background:#f5f7fa}.ds-demo-user span,.ds-demo-ai span{font-size:11px;font-weight:900;color:var(--ds-blue)}.ds-demo-user p,.ds-demo-ai p{color:#2d3b53;margin:5px 0}.ds-demo-ai small{display:block;margin-top:9px;color:#65748c}.ds-demo-user.compact{max-width:65%}.ds-pro{background:linear-gradient(135deg,#eef5ff 0,#f8f4ff 100%)!important}.ds-pro-card{display:grid;grid-template-columns:1.1fr .9fr;gap:48px;align-items:center;background:#fff;border:1px solid #dce6f4;border-radius:30px;padding:38px;box-shadow:0 24px 70px rgba(36,73,135,.1)}.ds-pro-copy p{font-size:17px}.ds-price-box{border:1px solid #dce5f2;background:#f8fbff;border-radius:24px;padding:26px;text-align:center}.ds-price-box>span{display:block;color:#64748b;font-size:12px;font-weight:900;text-transform:uppercase;letter-spacing:.08em}.ds-price-box>strong{display:block;font-size:52px;line-height:1.05;letter-spacing:-.04em;color:var(--ds-blue);margin:6px 0}.ds-price-box>small{display:block;font-weight:850;color:#24334d}.ds-price-next{margin:18px 0 14px;padding-top:16px;border-top:1px solid #dde6f1;color:#526079;font-size:13px}.ds-pro-button{width:100%}.ds-price-box>p{font-size:11px;color:#77849a;margin:10px 0 0}.ds-faq-list{max-width:850px;margin:auto;display:grid;gap:10px}.ds-faq-list details{background:#fff;border:1px solid var(--ds-line);border-radius:16px;padding:0 18px}.ds-faq-list summary{display:flex;justify-content:space-between;gap:18px;align-items:center;cursor:pointer;padding:16px 0;font-weight:850;list-style:none}.ds-faq-list summary::-webkit-details-marker{display:none}.ds-faq-list summary span{color:var(--ds-blue);font-size:22px}.ds-faq-list p{margin:0;padding:0 32px 18px 0}.ds-final{padding:64px 0;background:var(--ds-blue);color:#fff}.ds-final .ds-shell{display:flex;align-items:center;justify-content:space-between;gap:30px}.ds-final span{font-size:12px;font-weight:900;letter-spacing:.08em;text-transform:uppercase;color:#cfe0ff}.ds-final h2{font-size:clamp(27px,4vw,42px);line-height:1.1;letter-spacing:-.035em;max-width:760px;margin:8px 0 0}.ds-button-white{background:#fff;color:var(--ds-blue)!important;box-shadow:none;flex:none}.ds-button-white:hover{background:#edf4ff}.ds-footer{padding:35px 0;background:#081225;color:#c2cede}.ds-footer-main{display:flex;align-items:center;justify-content:space-between;gap:30px}.ds-footer .sos-logo-word b{color:#fff}.ds-footer-main nav{display:flex;flex-wrap:wrap;justify-content:flex-end;gap:12px 20px;font-size:12px}.ds-footer-main nav a:hover{color:#fff}.ds-footer-bottom{display:flex;justify-content:space-between;gap:20px;border-top:1px solid #20304b;margin-top:25px;padding-top:18px;font-size:11px;color:#8190a7}
@media(max-width:980px){.ds-nav{display:none}.ds-header-row{gap:14px}.ds-header-actions{margin-left:auto}.ds-menu-button{display:block}.ds-hero-grid,.ds-photo-grid,.ds-tutor-grid,.ds-check-grid,.ds-demo-grid,.ds-pro-card{grid-template-columns:1fr}.ds-hero-grid{gap:34px}.ds-feature-grid{grid-template-columns:1fr 1fr}.ds-scenario-grid{grid-template-columns:1fr 1fr}.ds-tutor-grid{gap:30px}.ds-photo-grid{gap:30px}.ds-demo-grid{gap:28px}.ds-pro-card{gap:24px}.ds-section{padding:66px 0}}
@media(max-width:640px){.ds-shell{width:min(100% - 28px,1160px)}.ds-header-row{height:61px}.ds-header-actions{display:none}.sos-logo-mark,.sos-logo-mark svg{width:34px;height:34px}.sos-logo-word{font-size:18px}.ds-hero{padding:31px 0 45px}.ds-hero-grid{gap:25px}.ds-badge{font-size:10px}.ds-hero h1{font-size:38px;margin:13px 0 14px}.ds-lead{font-size:16px;line-height:1.48}.ds-proof-row{margin-top:18px;gap:6px}.ds-proof-row span{font-size:11px;padding:7px 9px}.ds-solver-card{padding:12px;border-radius:20px}.ds-solver-top{padding-bottom:10px}.ds-ai-form textarea{min-height:112px;border-radius:14px;padding:13px 14px}.ds-attachments{flex-wrap:wrap}.ds-attach{font-size:12px}.ds-submit{min-height:50px}.ds-form-note{font-size:10.5px}.ds-answer{padding:14px;max-height:none}.ds-followup{grid-template-columns:1fr}.ds-section{padding:53px 0}.ds-section h2{font-size:31px}.ds-center-head{margin-bottom:25px}.ds-feature-grid,.ds-scenario-grid,.ds-exam-grid,.ds-steps,.ds-subject-mini{grid-template-columns:1fr}.ds-feature-grid{gap:10px}.ds-feature-grid article,.ds-scenario-grid article,.ds-exam-grid article,.ds-steps article{padding:18px}.ds-dropzone{min-height:205px}.ds-tutor-copy p{font-size:15px}.ds-subject-mini small{white-space:normal}.ds-check-grid{gap:25px}.ds-demo-user,.ds-demo-ai{max-width:94%}.ds-demo-user.compact{max-width:86%}.ds-pro-card{padding:22px;border-radius:23px}.ds-price-box>strong{font-size:46px}.ds-final{padding:46px 0}.ds-final .ds-shell{display:block}.ds-final .ds-button{margin-top:23px;width:100%}.ds-footer-main{display:block}.ds-footer-main nav{justify-content:flex-start;margin-top:20px}.ds-footer-bottom{display:block}.ds-footer-bottom span{display:block;margin:6px 0}.ds-mobile-menu>div{align-items:stretch;flex-direction:column}.ds-mobile-menu .ds-button{width:100%}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}.ds-button{transition:none}.ds-spinner{animation:none}}