.sb-3pn {
display: grid; grid-template-columns: 220px 260px 1fr;
min-height: 480px;
font-family: 'Inter', system-ui, -apple-system, sans-serif;
background: #181a1f; color: #d6d8de;
border-radius: 8px; overflow: hidden;
letter-spacing: -0.01em;
}
.sb-3pn-ws { background: #14161a; border-right: 1px solid rgba(255,255,255,0.05); padding: 16px 12px; display: flex; flex-direction: column; gap: 14px; }
.sb-3pn-brand { display: flex; align-items: center; gap: 10px; padding: 4px 6px 12px; border-bottom: 1px solid rgba(255,255,255,0.05); text-decoration: none; }
.sb-3pn-mark { width: 22px; height: 22px; flex-shrink: 0; border-radius: 5px; background: linear-gradient(135deg, #4d7cff 0%, #1850e0 100%); box-shadow: 0 4px 14px rgba(77,124,255,0.35); position: relative; }
.sb-3pn-mark::after { content: ''; position: absolute; inset: 5px; border: 1.5px solid #fff; border-radius: 1px; }
.sb-3pn-name { font-size: 14px; font-weight: 700; color: #fff; letter-spacing: -0.02em; }
.sb-3pn-shead { font-size: 10.5px; font-weight: 600; letter-spacing: 0.04em; color: #6a6e76; padding: 0 8px; margin-top: 4px; }
.sb-3pn-ws ul { list-style: none; margin: 0 0 8px; padding: 0; display: flex; flex-direction: column; gap: 1px; }
.sb-3pn-ws a {
display: flex; align-items: center; gap: 10px;
padding: 6px 10px; border-radius: 6px;
font-size: 13px; font-weight: 500; color: #b6b9c1; text-decoration: none;
transition: background 0.12s, color 0.12s;
}
.sb-3pn-ws a:hover { background: rgba(255,255,255,0.04); color: #fff; }
.sb-3pn-ws a[aria-current="page"] { background: rgba(77,124,255,0.16); color: #fff; box-shadow: inset 2px 0 0 #4d7cff; padding-left: 8px; }
.sb-3pn-i { width: 14px; text-align: center; flex-shrink: 0; font-size: 11px; color: #6a6e76; }
.sb-3pn-ws a[aria-current="page"] .sb-3pn-i { color: #4d7cff; }
.sb-3pn-ws a em { margin-left: auto; font-style: normal; font-size: 10.5px; font-weight: 600; color: #6a6e76; padding: 1px 6px; border-radius: 8px; background: rgba(255,255,255,0.06); }
.sb-3pn-ws a[aria-current="page"] em { background: rgba(77,124,255,0.2); color: #4d7cff; }
.sb-3pn-avatar { width: 18px; height: 18px; border-radius: 50%; flex-shrink: 0; display: flex; align-items: center; justify-content: center; font-size: 9.5px; font-weight: 700; color: #fff; }
.sb-3pn-list { background: #1a1c21; border-right: 1px solid rgba(255,255,255,0.05); display: flex; flex-direction: column; overflow: hidden; }
.sb-3pn-list header { display: flex; align-items: center; justify-content: space-between; padding: 14px 16px; border-bottom: 1px solid rgba(255,255,255,0.05); }
.sb-3pn-list h2 { margin: 0; font-size: 13px; font-weight: 700; color: #fff; letter-spacing: -0.01em; }
.sb-3pn-list button { width: 24px; height: 24px; border-radius: 5px; border: 0; background: rgba(255,255,255,0.05); color: #fff; font-size: 14px; cursor: pointer; transition: background 0.14s; }
.sb-3pn-list button:hover { background: #4d7cff; }
.sb-3pn-list ul { list-style: none; margin: 0; padding: 6px; display: flex; flex-direction: column; gap: 0; flex: 1; overflow-y: auto; }
.sb-3pn-list li { padding: 12px 12px; border-radius: 6px; cursor: pointer; transition: background 0.12s; border-bottom: 1px solid rgba(255,255,255,0.03); }
.sb-3pn-list li:hover { background: rgba(255,255,255,0.04); }
.sb-3pn-list li.active { background: rgba(77,124,255,0.1); border-bottom-color: transparent; box-shadow: inset 2px 0 0 #4d7cff; }
.sb-3pn-list strong { display: block; font-size: 13px; font-weight: 600; color: #fff; letter-spacing: -0.01em; }
.sb-3pn-list span { display: block; font-size: 11px; color: #6a6e76; margin-top: 4px; }
.sb-3pn-edit { padding: 32px 36px; overflow-y: auto; background: #181a1f; }
.sb-3pn-edit header { padding-bottom: 14px; border-bottom: 1px solid rgba(255,255,255,0.05); margin-bottom: 18px; }
.sb-3pn-eye { font-family: 'JetBrains Mono', monospace; font-size: 11px; color: #4d7cff; letter-spacing: 0.04em; }
.sb-3pn-edit h1 { margin: 4px 0 4px; font-size: clamp(28px, 4vw, 40px); font-weight: 700; color: #fff; letter-spacing: -0.03em; line-height: 1.05; }
.sb-3pn-edit header p { margin: 0; font-size: 12px; color: #6a6e76; }
.sb-3pn-body { margin: 0 0 18px; font-size: 14.5px; color: #d6d8de; line-height: 1.65; max-width: 540px; }
.sb-3pn-edit h2 { margin: 18px 0 8px; font-size: 16px; font-weight: 700; color: #fff; letter-spacing: -0.01em; }
.sb-3pn-edit ul { margin: 0 0 16px; padding-left: 22px; font-size: 13.5px; color: #b6b9c1; line-height: 1.75; }
@media (max-width: 720px) {
.sb-3pn { grid-template-columns: 1fr; }
.sb-3pn-ws, .sb-3pn-list { border-right: 0; border-bottom: 1px solid rgba(255,255,255,0.06); }
} <div class="sb-3pn">
<aside class="sb-3pn-ws" aria-label="Workspace">
<a class="sb-3pn-brand" href="#!">
<span class="sb-3pn-mark" aria-hidden="true"></span>
<span class="sb-3pn-name">Threads</span>
</a>
<nav aria-label="Workspace">
<span class="sb-3pn-shead">Workspace</span>
<ul>
<li><a href="#!" aria-current="page"><span class="sb-3pn-i" aria-hidden="true">▤</span>Notes<em>12</em></a></li>
<li><a href="#!"><span class="sb-3pn-i" aria-hidden="true">◇</span>Projects</a></li>
<li><a href="#!"><span class="sb-3pn-i" aria-hidden="true">◯</span>Calendar</a></li>
<li><a href="#!"><span class="sb-3pn-i" aria-hidden="true">▢</span>Archive</a></li>
</ul>
<span class="sb-3pn-shead">People</span>
<ul>
<li><a href="#!"><span class="sb-3pn-avatar" aria-hidden="true" style="background:#5b8eff">A</span>Anya</a></li>
<li><a href="#!"><span class="sb-3pn-avatar" aria-hidden="true" style="background:#ff7a4d">D</span>Daichi</a></li>
<li><a href="#!"><span class="sb-3pn-avatar" aria-hidden="true" style="background:#34c759">L</span>Lena</a></li>
</ul>
</nav>
</aside>
<aside class="sb-3pn-list" aria-label="Pages">
<header>
<h2>Notes</h2>
<button type="button" aria-label="New page">+</button>
</header>
<ul>
<li class="active">
<strong>Sprint 47 retro</strong>
<span>Yesterday · 14:21</span>
</li>
<li>
<strong>Hiring loop · Q3</strong>
<span>2 days ago</span>
</li>
<li>
<strong>Vendor shortlist</strong>
<span>Last week</span>
</li>
<li>
<strong>Team offsite ideas</strong>
<span>Apr 24</span>
</li>
<li>
<strong>OKR review · H1</strong>
<span>Apr 18</span>
</li>
</ul>
</aside>
<main class="sb-3pn-edit">
<header>
<span class="sb-3pn-eye">CMD + K to switch · ⌘1 / ⌘2 / ⌘3</span>
<h1>Sprint 47 retro.</h1>
<p>Last edited yesterday at 14:21 · 4 collaborators</p>
</header>
<p class="sb-3pn-body">Three independent panes, each with its own scroll. The workspace nav (left), the page list (middle), and the editor (right) — the shell behind Notion, Linear, Apple Notes.</p>
<h2>What went well</h2>
<ul>
<li>Shipped the dashboard refactor on time.</li>
<li>Onboarding flow completion up 18%.</li>
<li>Zero P0 incidents during launch week.</li>
</ul>
<h2>To improve</h2>
<ul>
<li>QA cycle compressed at the end — pull it earlier.</li>
<li>Marketing copy review needs a clearer owner.</li>
</ul>
</main>
</div>