:root {
  --online-blue: #2777f3;
  --online-ink: #2a5eb5;
  --online-purple: #21154a;
  --online-width: 1440px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; min-width: 320px; color: #2557a4; font-family: "Microsoft YaHei", "PingFang SC", Arial, sans-serif; background: #fff; }
button, a { font: inherit; }
button { cursor: pointer; }
img { display: block; max-width: 100%; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }

.online-header { position: absolute; inset: 0 0 auto; z-index: 10; width: min(1740px, calc(100% - 110px)); height: 100px; margin: auto; display: flex; align-items: center; justify-content: space-between; opacity: 0; }
.online-logo img { width: 68px; height: 62px; object-fit: contain; }
.online-nav { display: flex; align-items: center; gap: 12px; }
.online-nav a { min-width: 94px; padding: 9px 14px; border-radius: 20px; color: #64738c; font-size: 14px; text-align: center; text-decoration: none; transition: .2s ease; }
.online-nav a:hover, .online-nav a.active { color: #fff; background: var(--online-blue); box-shadow: 0 4px 10px #4d83e94d; }

.online-hero { position: relative; height: 746px; overflow: hidden; background: #f1f2fa url("线上学伴.png") center top / 1920px auto no-repeat; }
.hero-showcase { position: relative; z-index: 1; width: min(1740px, calc(100% - 160px)); height: 100%; margin: auto; padding: 0; display: block; }
.video-screen { position: absolute; top: 150px; left: 8px; width: 970px; height: 590px; overflow: hidden; padding: 0; border: 1px solid rgba(255, 255, 255, .72); border-radius: 4px; background: #dfe7f2; box-shadow: none; }
.video-screen video { width: 100%; height: 100%; display: block; object-fit: cover; background: #dfe7f2; }
.hero-message { display: none; }
.hero-message h1 { margin: 0; color: #1555b7; font-size: 31px; font-weight: 700; letter-spacing: 0; }
.hero-badge { width: fit-content; margin: 14px auto 0; padding: 5px 24px; border-radius: 20px; color: #fff; font-size: 12px; background: linear-gradient(90deg, #2473e8, #38a6f2); box-shadow: 0 4px 9px #287de933; }
.hero-version { margin: 54px 0 0; color: #4d75a6; font-size: 12px; }
.hero-details { display: flex; justify-content: space-between; gap: 30px; margin: 33px auto 0; color: #7890ad; font-size: 10px; line-height: 1.8; text-align: left; }
.hero-details p { width: 50%; margin: 0; }

@media (min-width: 1201px) {
  .online-hero::after {
    position: absolute;
    z-index: 0;
    inset: 0 0 auto;
    height: 132px;
    content: "";
    pointer-events: none;
    background: linear-gradient(100deg, #f8fbfc 0%, #f4f7fa 55%, #d8e4ef 100%);
    -webkit-mask-image: linear-gradient(#000 0 72%, transparent 100%);
    mask-image: linear-gradient(#000 0 72%, transparent 100%);
  }
}

.join-banner { width: min(1430px, calc(100% - 190px)); height: 360px; margin: 110px auto 100px; padding: 0 50px 0 0; display: grid; grid-template-columns: 420px 1fr 205px; align-items: center; gap: 68px; background: #f2f7ff; box-shadow: 0 0 0 1px #e2eaf7, 0 8px 20px #cad8ed40; }
.join-banner-photo { height: 360px; overflow: hidden; }
.join-banner-photo img { width: 100%; height: 100%; object-fit: cover; }
.join-banner-copy strong { display: block; color: #182f58; font-size: 28px; }
.join-banner-copy h2 { margin: 4px 0 12px; color: #182f58; font-size: 28px; }
.join-banner-copy p { max-width: 520px; margin: 0; color: #8290a4; font-size: 13px; line-height: 1.8; }
.join-banner-button { display: flex; height: 66px; align-items: center; justify-content: center; border-radius: 3px; color: #fff; font-size: 15px; text-decoration: none; background: var(--online-blue); box-shadow: 0 8px 20px #347df14d; }

.services { min-height: 1120px; padding: 180px 0 120px; background: #fff; }
.section-heading { width: fit-content; margin: 0 auto 78px; text-align: center; }
.section-heading span { display: block; color: #b7d8fd; font-size: 14px; font-weight: 700; letter-spacing: 1px; }
.section-heading strong { position: relative; display: block; margin-top: 5px; color: #2f7df0; font-size: 25px; }
.section-heading strong::before, .section-heading strong::after { content: ""; position: absolute; top: 50%; width: 175px; height: 1px; background: linear-gradient(90deg, transparent, #badbff); }
.section-heading strong::before { right: calc(100% + 18px); }
.section-heading strong::after { left: calc(100% + 18px); transform: rotate(180deg); }
.services-layout { width: min(1440px, calc(100% - 220px)); margin: auto; display: grid; grid-template-columns: 445px 1fr; gap: 105px; align-items: center; }
.service-tabs { display: grid; gap: 28px; }
.service-tabs button { width: 410px; height: 108px; padding: 0; border: 0; background: transparent; opacity: .82; transition: transform .2s, opacity .2s; }
.service-tabs button:hover, .service-tabs button.selected { opacity: 1; transform: translateX(8px); }
.service-tabs img { width: 100%; height: 100%; object-fit: contain; }
.study-collage { position: relative; width: 760px; height: 760px; }
.study-photo { position: absolute; width: 285px; height: 285px; overflow: hidden; border-radius: 4px; }
.study-photo img { width: 100%; height: 100%; object-fit: cover; }
.photo-one { top: 0; left: 0; }.photo-two { top: 0; right: 0; }.photo-three { bottom: 0; left: 0; }.photo-four { right: 0; bottom: 0; }
.device-orbit { position: absolute; top: 50%; left: 50%; width: 280px; height: 280px; transform: translate(-50%, -50%); }
.orbit-bg, .device-image { position: absolute; inset: 0; width: 100%; height: 100%; object-fit: contain; }

.dsa-section { min-height: 1110px; padding: 95px 0 120px; background: #f7f7f8; }
.dsa-card { width: min(1420px, calc(100% - 200px)); margin: auto; border-radius: 18px; overflow: hidden; box-shadow: 0 12px 30px #aeb4c633; }
.dsa-card img { width: 100%; height: auto; }

.outcomes { position: relative; height: 1004px; min-height: 0; padding: 0; overflow: hidden; background: #fff url("线上学伴.png") center -3546px / 1920px auto no-repeat; }
.outcomes > * { visibility: hidden; }
.outcomes .section-heading { margin-bottom: 24px; }
.outcomes-lead { width: min(760px, calc(100% - 40px)); margin: 0 auto; color: #c5d2e3; font-size: 14px; line-height: 2; text-align: center; }
.outcomes-stage { width: min(1920px, 100%); margin: 125px auto 0; display: grid; grid-template-columns: 1fr 150px 1fr; align-items: center; }
.outcome-block { height: 420px; display: grid; grid-template-rows: 1fr 1fr; background-size: 100% 100%; background-position: center; background-repeat: no-repeat; }
.outcome-blue { background-image: url("线上伴学/矩形 96.png"); }.outcome-red { background-image: url("线上伴学/矩形 104.png"); }
.outcome-block div { display: flex; flex-direction: column; align-items: center; justify-content: center; color: #fff; text-align: center; }
.outcome-block strong { font-size: 27px; }.outcome-block span { margin-top: 7px; font-size: 12px; }
.refresh-mark { width: 115px; height: 115px; margin: auto; object-fit: contain; opacity: .62; }

.retention-banner { position: relative; height: 310px; display: flex; flex-direction: column; align-items: center; justify-content: center; color: #fff; text-align: center; background: var(--online-purple) url("线上学伴.png") center -4550px / 1920px auto no-repeat; }
.retention-banner > * { visibility: hidden; }
.retention-banner::before, .retention-banner::after, .retention-banner .banner-triangle { display: none; }
.retention-banner::before, .retention-banner::after { content: ""; position: absolute; top: 50%; width: 32%; height: 2px; background: #433766; }.retention-banner::before { left: 7%; }.retention-banner::after { right: 7%; }
.retention-banner p { position: relative; z-index: 1; margin: 0 0 17px; font-size: 25px; font-weight: 700; }.retention-banner p strong { color: #28c9ed; }.retention-banner small { color: #aaa1c4; font-size: 11px; }
.banner-triangle { position: absolute; z-index: 2; top: 50%; width: 0; height: 0; transform: translateY(-50%); border-top: 7px solid transparent; border-bottom: 7px solid transparent; }.banner-triangle.left { left: 29%; border-right: 11px solid #fff; }.banner-triangle.right { right: 29%; border-left: 11px solid #fff; }

.cases { min-height: 2180px; padding: 170px 0 120px; background: #fff; }.cases .section-heading { margin-bottom: 25px; }.cases-lead { margin: 0 auto 65px; color: #c8d2df; font-size: 13px; text-align: center; }
.case-phones { width: min(1420px, calc(100% - 220px)); margin: auto; display: grid; grid-template-columns: 1fr 1fr; gap: 115px; align-items: end; }
.phone-group { height: 590px; display: flex; justify-content: center; align-items: center; gap: 20px; }.phone-group img { width: 155px; height: 420px; object-fit: contain; }.phone-light img:nth-child(2) { transform: translateY(-22px); }.phone-light img:nth-child(3) { transform: translateY(14px); }.phone-dark img { width: 205px; height: 500px; }.phone-dark { gap: 30px; }
.case-chat-grid { width: min(1330px, calc(100% - 220px)); min-height: 900px; margin: 80px auto 0; padding: 55px 65px; display: grid; grid-template-columns: 1fr 1fr; gap: 35px; border-radius: 13px; background: #f6f6f7; }.case-chat-grid img { width: 100%; height: 330px; object-fit: cover; border-radius: 10px; box-shadow: 0 6px 18px #aeb7c22e; }

.case-poster { padding: 75px 0 85px; background: #f6f8fb; }.case-poster img { width: min(1840px, calc(100% - 80px)); margin: auto; border: 10px solid #fff; border-radius: 16px; box-shadow: 0 6px 15px #68778e45; }
.online-join { min-height: 300px; padding: 78px 20px; color: #fff; text-align: center; background: #216bf1; }.online-join p { margin: 0 0 18px; font-size: 17px; }.online-join strong { display: block; font-size: 18px; }.online-join a { display: inline-block; margin-top: 25px; padding: 11px 18px; border-radius: 20px; color: #1762e5; font-size: 13px; font-weight: 700; text-decoration: none; background: #fff; }
.online-footer { min-height: 245px; padding: 54px max(80px, calc((100% - 1700px) / 2)); display: grid; grid-template-columns: 1.3fr 1fr 1fr; gap: 80px; color: #fff; background: #11082f; }.footer-brand, .footer-contact, .footer-qr { min-height: 130px; }.footer-brand { display: flex; align-items: center; gap: 32px; }.footer-brand img { width: 68px; height: 62px; }.footer-brand p, .footer-contact p { color: #d8d5e6; font-size: 12px; line-height: 1.8; }.footer-contact, .footer-qr { padding-left: 45px; border-left: 1px solid #342a5a; }.online-footer h2 { margin: 0 0 24px; font-size: 15px; }.footer-contact { display: flex; flex-wrap: wrap; gap: 12px 40px; }.footer-contact h2 { flex-basis: 100%; }.footer-qr img { display: inline-block; width: 78px; height: 78px; margin-right: 14px; background: #fff; }.floating-contact { position: fixed; z-index: 20; right: 0; top: 52%; padding: 10px 15px 10px 16px; border-radius: 25px 0 0 25px; color: #fff; font-size: 13px; text-decoration: none; background: #164ca9; box-shadow: 0 3px 12px #174da966; }

@media (max-width: 1200px) { .online-header { width: calc(100% - 50px); opacity: 1; }.online-hero { height: 760px; background: radial-gradient(circle at 77% 44%, #d9efff 0, #eef9ff 28%, transparent 52%), linear-gradient(150deg, #f8fcff 0%, #deefff 64%, #b9d9ff 100%); }.hero-showcase { width: calc(100% - 80px); padding-top: 148px; display: grid; grid-template-columns: 1fr 1fr; gap: 35px; }.video-screen { position: relative; top: auto; left: auto; width: auto; height: 530px; border: 1px solid #dfe9f6; background: #dfe7f2; box-shadow: 0 22px 50px #a8c2e64a; }.hero-message { display: block; padding-top: 67px; }.join-banner { width: calc(100% - 80px); grid-template-columns: 32% 1fr 150px; gap: 30px; }.services-layout { width: calc(100% - 80px); grid-template-columns: 38% 1fr; gap: 30px; }.service-tabs button { width: 100%; }.study-collage { width: 100%; height: auto; aspect-ratio: 1; }.study-photo { width: 38%; height: 38%; }.dsa-card { width: calc(100% - 80px); }.case-phones, .case-chat-grid { width: calc(100% - 80px); }.case-poster img { width: calc(100% - 40px); } }
@media (max-width: 760px) { .online-header { position: fixed; width: 100%; height: 68px; padding: 0 18px; background: #ffffffed; box-shadow: 0 2px 12px #5071a31c; }.online-logo img { width: 50px; height: 46px; }.online-nav { gap: 0; overflow-x: auto; }.online-nav a { min-width: auto; padding: 7px 8px; font-size: 11px; }.online-hero { height: auto; padding: 110px 20px 60px; background: radial-gradient(circle at 77% 44%, #d9efff 0, #eef9ff 28%, transparent 52%), linear-gradient(150deg, #f8fcff 0%, #deefff 64%, #b9d9ff 100%); }.hero-showcase { width: 100%; padding: 0; display: block; }.video-screen { position: relative; top: auto; left: auto; width: 100%; height: auto; aspect-ratio: 16 / 9; background: #dfe7f2; box-shadow: 0 22px 50px #a8c2e64a; }.hero-message { display: block; padding: 45px 5px 0; }.hero-message h1 { font-size: 25px; }.hero-badge { font-size: 10px; }.hero-version { margin-top: 35px; font-size: 10px; }.hero-details { margin-top: 22px; display: block; font-size: 9px; }.hero-details p { width: 100%; margin-top: 4px; }.join-banner { width: calc(100% - 30px); height: auto; margin: 45px auto 65px; padding: 0 18px 22px; display: block; }.join-banner-photo { height: 185px; margin: 0 -18px 25px; }.join-banner-copy strong, .join-banner-copy h2 { font-size: 20px; }.join-banner-button { height: 46px; margin-top: 22px; }.services { min-height: auto; padding: 115px 15px 70px; }.section-heading { margin-bottom: 45px; }.section-heading strong { font-size: 21px; }.section-heading strong::before, .section-heading strong::after { width: 45px; }.services-layout { width: 100%; display: flex; flex-direction: column; gap: 45px; }.service-tabs { width: 100%; gap: 12px; }.service-tabs button { width: 100%; height: auto; aspect-ratio: 830 / 218; }.service-tabs button:hover, .service-tabs button.selected { transform: none; }.study-collage { width: min(100%, 390px); }.dsa-section { min-height: auto; padding: 35px 15px 55px; }.dsa-card { width: 100%; }.outcomes { min-height: auto; padding: 105px 15px 80px; }.outcomes-stage { margin-top: 60px; grid-template-columns: 1fr; gap: 18px; }.outcome-block { height: 180px; }.refresh-mark { width: 65px; height: 65px; }.retention-banner { height: 215px; padding: 0 30px; }.retention-banner p { font-size: 18px; }.retention-banner::before, .retention-banner::after { width: 18%; }.banner-triangle.left { left: 20%; }.banner-triangle.right { right: 20%; }.cases { min-height: auto; padding: 110px 15px 70px; }.case-phones { width: 100%; display: block; }.phone-group { height: auto; margin-bottom: 30px; gap: 8px; }.phone-group img { width: 29%; height: auto; }.phone-dark img { width: 40%; height: auto; }.case-chat-grid { width: 100%; min-height: auto; margin-top: 35px; padding: 15px; gap: 12px; }.case-chat-grid img { height: 130px; }.case-poster { padding: 30px 0; }.case-poster img { width: calc(100% - 20px); border-width: 5px; border-radius: 10px; }.online-join { min-height: 240px; padding: 55px 20px; }.online-join p { font-size: 15px; }.online-join strong { font-size: 13px; }.online-footer { padding: 40px 25px; display: block; }.online-footer .footer-brand, .online-footer .footer-contact, .online-footer .footer-qr { margin-bottom: 30px; padding-left: 0; border-left: 0; }.floating-contact span { display: none; } }

@media (max-width: 760px) { .outcomes { height: auto; background: #fff; }.outcomes > * { visibility: visible; }.retention-banner { background: var(--online-purple); }.retention-banner > * { visibility: visible; }.retention-banner::before, .retention-banner::after, .retention-banner .banner-triangle { display: block; } }

@media (min-width: 761px) and (max-width: 1200px) {
  .case-phones {
    grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
    gap: 32px;
  }

  .phone-group {
    min-width: 0;
    height: 440px;
    gap: 10px;
  }

  .phone-group img {
    width: calc((100% - 20px) / 3);
    height: 360px;
  }

  .phone-dark { gap: 16px; }
  .phone-dark img {
    width: calc((100% - 16px) / 2);
    height: 410px;
  }

  .case-chat-grid {
    padding: 36px 40px;
    gap: 22px;
  }
}