:root {
    --guide-primary: #667eea;
    --guide-secondary: #764ba2;
    --guide-ink: #1a202c;
    --guide-muted: #64748b;
    --guide-border: #e7eaf3;
    --guide-surface: #ffffff;
    --guide-bg: #f7f8fc;
    --guide-shadow: 0 24px 70px rgba(45, 55, 110, 0.14);
}

* { box-sizing: border-box; }
html { min-width: 320px; }
body { margin: 0; color: var(--guide-ink); background: var(--guide-bg); font-family: 'Inter', sans-serif; }
a { color: inherit; text-decoration: none; }
button { font: inherit; }

.guide-header { height: 80px; background: rgba(255, 255, 255, 0.94); border-bottom: 1px solid var(--guide-border); position: relative; z-index: 2; }
.guide-nav { height: 100%; max-width: 1500px; margin: auto; padding: 0 4vw; display: flex; align-items: center; justify-content: space-between; }
.brand { display: flex; align-items: center; gap: 10px; color: var(--guide-primary); font-size: 1.45rem; font-weight: 800; }
.brand i { font-size: 1.7rem; background: linear-gradient(135deg, var(--guide-primary), var(--guide-secondary)); background-clip: text; color: transparent; }
.nav-actions { display: flex; align-items: center; gap: 24px; color: var(--guide-muted); font-size: .92rem; font-weight: 600; }
.back-link:hover, .login-link:hover { color: var(--guide-primary); }
.trial-link { color: white; padding: 11px 19px; border-radius: 10px; background: linear-gradient(135deg, var(--guide-primary), var(--guide-secondary)); box-shadow: 0 8px 18px rgba(102, 126, 234, .2); }
.guide-main { max-width: 1500px; margin: auto; padding: clamp(22px, 2.5vw, 38px) 4vw 70px; }
.guide-intro { display: flex; justify-content: space-between; align-items: end; gap: 32px; margin-bottom: clamp(28px, 4vw, 56px); }
.eyebrow { display: inline-flex; gap: 9px; align-items: center; color: var(--guide-primary); font-size: .78rem; font-weight: 800; letter-spacing: .1em; text-transform: uppercase; }
.guide-intro h1 { margin: 8px 0 8px; font-size: clamp(1.8rem, 3vw, 3.2rem); line-height: 1.05; letter-spacing: -.04em; }
.guide-intro p { max-width: 620px; margin: 0; color: var(--guide-muted); font-size: clamp(1rem, 1.4vw, 1.2rem); }
.desktop-notice { display: none; align-items: center; gap: 14px; max-width: 350px; padding: 16px 19px; border: 1px solid #dbe2ff; border-radius: 12px; background: #f2f4ff; color: #4653a2; font-size: .84rem; }
.desktop-notice i { font-size: 1.45rem; }
.desktop-notice strong, .desktop-notice span { display: block; }
.desktop-notice strong { margin-bottom: 3px; font-size: .9rem; color: #303d8c; }
.tutorial-layout { display: grid; grid-template-columns: minmax(300px, 390px) minmax(0, 1fr); min-height: min(820px, calc(100vh - 175px)); background: var(--guide-surface); border: 1px solid var(--guide-border); border-radius: 18px; overflow: hidden; box-shadow: var(--guide-shadow); }
.tutorial-sidebar { padding: 24px 0; border-right: 1px solid var(--guide-border); background: #fbfbfe; }
.sidebar-heading { display: flex; justify-content: space-between; align-items: center; padding: 0 24px 17px; color: var(--guide-ink); font-size: .84rem; font-weight: 800; text-transform: uppercase; letter-spacing: .06em; }
.tutorial-count { color: var(--guide-primary); font-size: .72rem; }
.tutorial-list { display: flex; flex-direction: column; }
.tutorial-item { width: 100%; display: grid; grid-template-columns: 86px minmax(0, 1fr) 16px; gap: 13px; align-items: center; padding: 12px 21px 12px 24px; border: 0; border-left: 3px solid transparent; background: transparent; color: var(--guide-ink); text-align: left; cursor: pointer; transition: background .2s ease, border-color .2s ease; }
.tutorial-item:hover { background: #f0f2ff; }
.tutorial-item.is-active { border-left-color: var(--guide-primary); background: #eef0ff; }
.tutorial-item img { width: 86px; aspect-ratio: 16 / 9; border-radius: 7px; object-fit: cover; }
.tutorial-item span { min-width: 0; }
.tutorial-item strong, .tutorial-item small { display: block; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.tutorial-item strong { font-size: .86rem; line-height: 1.3; }
.tutorial-item small { margin-top: 5px; color: var(--guide-muted); font-size: .72rem; }
.tutorial-item > i { color: #aab2c7; font-size: .72rem; }
.tutorial-item.is-active > i { color: var(--guide-primary); }
.player-panel { min-width: 0; display: flex; flex-direction: column; padding: clamp(18px, 2.5vw, 34px); background: #fff; }
.player-topline { display: flex; justify-content: space-between; gap: 16px; margin-bottom: 16px; color: var(--guide-muted); font-size: .75rem; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; }
.player-topline i { color: #52c41a; font-size: .55rem; vertical-align: 2px; }
.video-frame { flex: 1; min-height: 0; display: flex; align-items: center; justify-content: center; overflow: hidden; border-radius: 12px; background: #101522; box-shadow: 0 16px 35px rgba(15, 23, 42, .18); }
.video-frame video { display: block; width: 100%; max-height: 100%; aspect-ratio: 16 / 9; object-fit: contain; background: #101522; }
.player-caption { display: flex; align-items: center; gap: 15px; padding-top: 23px; }
.video-number { display: grid; width: 43px; height: 43px; flex-shrink: 0; place-items: center; color: var(--guide-primary); border: 1px solid #dce1ff; border-radius: 50%; font-size: .8rem; font-weight: 800; }
.player-caption h2 { margin: 0 0 4px; font-size: clamp(1.1rem, 1.8vw, 1.55rem); }
.player-caption p { margin: 0; color: var(--guide-muted); font-size: .86rem; }

@media (max-width: 900px) {
    .guide-intro { align-items: start; flex-direction: column; }
    .desktop-notice { max-width: none; }
    .tutorial-layout { grid-template-columns: 300px minmax(0, 1fr); }
    .tutorial-item { grid-template-columns: 72px minmax(0, 1fr) 12px; gap: 9px; padding-left: 16px; padding-right: 13px; }
    .tutorial-item img { width: 72px; }
    .sidebar-heading { padding-left: 16px; padding-right: 16px; }
}

@media (max-width: 700px) {
    .guide-header { height: 68px; }
    .guide-nav { padding: 0 20px; }
    .nav-actions { gap: 12px; }
    .back-link, .login-link { display: none; }
    .trial-link { padding: 9px 13px; font-size: .8rem; }
    .guide-main { padding: 32px 16px 40px; }
    .guide-intro { margin-bottom: 20px; }
    .guide-intro h1 { font-size: 2rem; }
    .desktop-notice { display: flex; width: 100%; }
    .tutorial-layout { display: flex; flex-direction: column; min-height: 0; border-radius: 13px; }
    .tutorial-sidebar { order: 2; border-top: 1px solid var(--guide-border); border-right: 0; }
    .player-panel { order: 1; padding: 14px; }
    .video-frame { flex: none; }
    .player-caption { padding: 16px 2px 4px; }
    .tutorial-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 2px; }
    .tutorial-item { grid-template-columns: 58px minmax(0, 1fr); gap: 8px; padding: 9px 10px; border-left: 0; border-top: 3px solid transparent; }
    .tutorial-item.is-active { border-top-color: var(--guide-primary); }
    .tutorial-item img { width: 58px; }
    .tutorial-item > i { display: none; }
    .tutorial-item strong { font-size: .72rem; }
    .tutorial-item small { font-size: .64rem; }
    .sidebar-heading { padding-top: 18px; }
}

@media (max-width: 400px) {
    .tutorial-list { grid-template-columns: 1fr; }
}