:root { color-scheme: light; --ink: #162033; --muted: #5c667a; --blue: #0969da; --pale: #eef5ff; --line: #d8dee9; --paper: #ffffff; --navy: #081a38; }
* { box-sizing: border-box; }
body { margin: 0; color: var(--ink); background: #f7f9fc; font: 16px/1.55 Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; }
a { color: var(--blue); }
.skip-link { position: absolute; left: -999px; top: 0; background: white; padding: .75rem; z-index: 10; }
.skip-link:focus { left: 1rem; }
.hero { color: white; background: radial-gradient(circle at 85% 10%, #205bb7 0, transparent 36%), linear-gradient(135deg, var(--navy), #0d326a); padding: 0 5vw 4.5rem; }
.topbar { display: flex; align-items: center; justify-content: space-between; max-width: 1180px; margin: auto; padding: 1.25rem 0; }
.topbar a { color: white; text-decoration: none; }
.brand-lockup { display: flex; align-items: center; gap: .75rem; }
.oneplus-mark { display: grid; place-items: center; width: 52px; height: 52px; padding: .35rem; flex: 0 0 auto; background: white; border-radius: .7rem; box-shadow: 0 8px 24px rgba(0, 0, 0, .2); }
.oneplus-mark img { display: block; width: 100%; height: 100%; object-fit: contain; }
.brand { display: grid; gap: .05rem; font-weight: 800; line-height: 1.2; }
.brand-kicker { color: #9ee5ff; font-size: .66rem; font-weight: 800; letter-spacing: .08em; text-transform: uppercase; }
.brand strong { font-size: 1rem; }
.nav-links { display: flex; flex-wrap: wrap; justify-content: flex-end; gap: 1.25rem; }
.hero-grid { max-width: 1180px; margin: 4rem auto 0; display: grid; grid-template-columns: 1.25fr .75fr; gap: 4rem; align-items: center; }
.hero-grid a:not(.primary) { color: #b9e9ff; }
.eyebrow { margin: 0 0 .4rem; color: #67d5ff; text-transform: uppercase; letter-spacing: .12em; font-size: .75rem; font-weight: 800; }
h1 { max-width: 760px; margin: 0; font-size: clamp(2.5rem, 6vw, 5rem); line-height: 1.02; letter-spacing: -.045em; }
.lead { max-width: 760px; color: #dbe8ff; font-size: 1.12rem; margin: 1.4rem 0 2rem; }
.primary, .secondary { display: inline-block; border: 0; border-radius: .6rem; padding: .8rem 1rem; font: inherit; font-weight: 800; text-decoration: none; cursor: pointer; }
.primary { color: #082653; background: #74dcff; }
.secondary { color: white; background: var(--blue); }
.model { display: grid; grid-template-columns: 1fr auto 1fr; gap: .75rem; align-items: center; }
.model span { padding: 1rem; border: 1px solid #5d84bd; border-radius: .75rem; text-align: center; background: #0d2e5c; }
.overview, .workspace { max-width: 1180px; margin: auto; }
.overview { display: flex; justify-content: space-between; gap: 2rem; align-items: end; padding: 3.5rem 0 2rem; }
.overview .eyebrow, .lesson-panel .eyebrow { color: var(--blue); }
h2 { margin: 0; font-size: clamp(1.65rem, 3vw, 2.4rem); }
progress { display: block; margin-top: .5rem; width: 240px; accent-color: var(--blue); }
.workspace { display: grid; grid-template-columns: 320px 1fr; gap: 1.25rem; padding-bottom: 5rem; }
.workspace aside, .lesson-panel { border: 1px solid var(--line); background: var(--paper); border-radius: 1rem; box-shadow: 0 16px 40px rgba(9, 32, 67, .06); }
.workspace aside { padding: 1rem; align-self: start; }
.filters { display: flex; gap: .35rem; flex-wrap: wrap; padding-bottom: .9rem; }
.filter, .tab { border: 1px solid var(--line); background: white; border-radius: 999px; padding: .45rem .7rem; cursor: pointer; }
.filter.active, .tab.active { color: white; background: var(--blue); border-color: var(--blue); }
.lesson-list { display: grid; gap: .5rem; }
.lesson-link { display: grid; gap: .1rem; width: 100%; padding: .8rem; text-align: left; border: 1px solid transparent; border-radius: .7rem; background: transparent; cursor: pointer; }
.lesson-link:hover, .lesson-link.active { background: var(--pale); border-color: #b9d5fa; }
.lesson-link span, .lesson-link small { color: var(--muted); text-transform: capitalize; }
.lesson-panel { min-height: 510px; padding: 2rem; }
.lesson-heading { display: flex; justify-content: space-between; gap: 1rem; }
.complete-control { white-space: nowrap; }
.lesson-summary { max-width: 780px; color: var(--muted); font-size: 1.08rem; }
.tabs { display: flex; gap: .5rem; border-bottom: 1px solid var(--line); padding: 1.3rem 0 .8rem; }
.tab-content { padding-top: 1.25rem; }
.tab-content li { margin: .5rem 0; }
.tab-content fieldset { display: grid; gap: .7rem; margin: 1rem 0; border: 1px solid var(--line); border-radius: .75rem; padding: 1rem; }
.resource-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: .8rem; }
.resource-grid a { display: grid; padding: 1rem; border: 1px solid var(--line); border-radius: .75rem; text-decoration: none; }
.resource-grid span { color: var(--muted); }
footer { display: flex; justify-content: space-between; gap: 2rem; align-items: center; padding: 2rem 5vw; color: #dce7fa; background: var(--navy); }
.oneplus { display: flex; gap: .8rem; align-items: center; color: white; text-decoration: none; }
.oneplus img { width: 42px; height: 42px; object-fit: contain; background: white; border-radius: .4rem; }
.oneplus span { display: grid; }
.oneplus small { color: #aebdd5; }
footer p { max-width: 680px; }
@media (max-width: 800px) { .topbar, .hero-grid, .workspace { grid-template-columns: 1fr; } .topbar { align-items: start; flex-direction: column; gap: 1rem; } .model { margin-top: 1rem; } .overview, footer { align-items: start; flex-direction: column; } .overview, .workspace { margin-left: 1rem; margin-right: 1rem; } .resource-grid { grid-template-columns: 1fr; } .nav-links { justify-content: flex-start; gap: .6rem; font-size: .85rem; } }