:root { --bg:#0f0f10; --fg:#e8e8ea; --muted:#a9adb7; --card:#15161a; --border:#2b2f36; --accent:#4c8df6; --good:#42b883; --danger:#e66; --warn:#f4b400; --header-h:50px; }
    *{box-sizing:border-box}
    html,body{height:100%}
    body{ margin:0;background:var(--bg);color:var(--fg); font:14px/1.4 system-ui,-apple-system,Segoe UI,Roboto,Inter,Arial,sans-serif; display:flex;flex-direction:column;overflow:hidden; }
    header{ display:flex;gap:8px;align-items:center;padding:10px;border-bottom:1px solid var(--border); position:sticky;top:0;background:var(--bg);z-index:5; }
    input,select,button,textarea{ background:var(--card);color:var(--fg);border:1px solid var(--border); border-radius:8px;padding:8px 10px;outline:none; }
    button{cursor:pointer}
    button.primary{ background: rgba(76,141,246,.16); border-color: rgba(76,141,246,.45) }
    button.primary:hover{ background: rgba(76,141,246,.24) }
    button.good{ background: rgba(66,184,131,.14); border-color: rgba(66,184,131,.38) }
    button.danger{ background: rgba(238,102,102,.14); border-color: rgba(238,102,102,.40) }
    button:disabled{ opacity:.6;cursor:not-allowed }
    .pill{padding:2px 8px;border:1px solid var(--border);border-radius:999px;font-size:12px}
    .hint{font-size:12px;color:var(--muted)}
    .badge{font-size:12px;color:#ccc}
    .hr{height:1px;background:var(--border);margin:8px 0}

    #wrap{ --side-w:320px; height:calc(100dvh - var(--header-h)); display:grid; grid-template-columns:var(--side-w) 1fr; min-height:0; }
    #side{ position:relative; border-right:1px solid var(--border); padding:12px; display:flex;flex-direction:column;gap:10px; width:var(--side-w); overflow-y:auto; }
    .panel{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:10px}

    #main{display:flex;flex-direction:column;min-height:0}
    #main-header{flex:0 0 auto;position:sticky;top:0;z-index:1;background:var(--bg);border-bottom:1px solid var(--border);padding:12px}
    #main-scroll{flex:1 1 auto;overflow:auto;padding:12px}

    /* Meta grid */
    .meta-grid{ display:flex;flex-direction:column;gap:10px;margin-top:10px }
    .field{ display:flex;flex-direction:column;gap:6px }

    /* Lessons */
    .toolrow { display:flex; gap:8px; align-items:center; flex-wrap:wrap; margin-bottom:10px }
    .lessons{ display:block; margin-top:8px }
    .lesson{ display:grid; grid-template-columns: 44px 56px 1fr auto; gap:8px; align-items:center; padding:8px; border:1px solid var(--border); border-radius:10px; margin-bottom:8px; background:rgba(255,255,255,.02); }
    .lesson.dragging{ opacity:.7; outline:2px dashed var(--accent) }
    .handle{ cursor:grab; user-select:none; font-weight:700; text-align:center; }
    .ltitle{ overflow:hidden; white-space:nowrap; text-overflow:ellipsis; }
    .ltools{ display:flex; gap:6px; }
    .lsub { color: var(--muted); font-size: 12px; }
    .thumb{
      width:48px;height:48px;
      object-fit:cover;
      border-radius:8px;
      background:#000;
      border:1px solid var(--border);
    }
    /* Mobile */
    @media (max-width:900px){
      #wrap{grid-template-columns:1fr}
      #side{ position:fixed;left:0;top:var(--header-h);bottom:0;width:min(86vw,360px); transform:translateX(-100%);transition:transform .2s ease; box-shadow:0 10px 24px rgba(0,0,0,.4);z-index:4; }
      body.sidebar-open #side{ transform:translateX(0) }
      #backdrop{ position:fixed;inset:var(--header-h) 0 0 0;background:rgba(0,0,0,.4); opacity:0;pointer-events:none;transition:opacity .2s ease;z-index:3 }
      body.sidebar-open #backdrop{opacity:1;pointer-events:auto}
      #open-side{ display:inline-flex;align-items:center;justify-content:center;width:28px;height:28px;margin-right:6px; border-radius:999px;background:var(--card);border:1px solid var(--border); }
      header{flex-wrap:wrap;gap:6px 8px}
      header input,header select,header button{flex:1 1 auto;min-width:0;width:auto !important}
      #in-course{flex-basis:100%}
    }

    @media (max-width:900px){
      /* make sidebar overlay header */
      #side{ z-index: 6; }
      #backdrop{ z-index: 5; }

      /* prevent lesson row overflow */
      .lesson{ grid-template-columns: 36px 44px 1fr; }
      .ltools{
        grid-column: 1 / -1;
        justify-content: flex-end;
        flex-wrap: wrap;
        gap: 6px 8px;
      }
    }


    /* Hide app until a course is loaded */
    body[data-has-course="false"] #wrap { display: none; }

    .iconbtn{
      width:28px;height:28px;
      display:inline-flex;align-items:center;justify-content:center;
      border:1px solid var(--border);
      border-radius:8px;
      background:var(--card);
      color:var(--fg);
      padding:0;
    }
    .iconbtn:hover{ border-color: var(--accent); }
    .iconbtn svg{ width:16px;height:16px; display:block }
    .iconbtn.danger{
      background: rgba(238,102,102,.12);
      border-color: rgba(238,102,102,.40);
    }
    .iconbtn.danger:hover{ background: rgba(238,102,102,.18); }

    /* Course Gate (overlay shown when no course is loaded) */
    #course-gate{
      position:fixed; inset:0;
      display:none; /* toggled via .show */
      align-items:center; justify-content:center;
      background:rgba(0,0,0,.55);
      z-index: 999; /* above header and sidebar */
    }
    #course-gate.show{ display:flex; }

    .gate-card{
      width:min(680px, 92vw);
      max-height:min(86vh, 800px);
      overflow:auto;
      background:var(--card);
      border:1px solid var(--border);
      border-radius:14px;
      padding:14px;
      box-shadow:0 12px 36px rgba(0,0,0,.5);
    }
    .gate-title{ display:flex; align-items:center; gap:10px; }
    .gate-title strong{ font-size:16px }
    .gate-hr{ height:1px; background:var(--border); margin:10px 0 }

    .gate-grid{ display:grid; grid-template-columns:1fr; gap:10px; }
    .gate-row{ display:flex; gap:8px; align-items:center; flex-wrap:wrap; }
    .gate-row > *{ flex:1 1 auto; min-width:0 }
    .gate-actions{ display:flex; gap:8px; justify-content:flex-end; flex-wrap:wrap; }
    .gate-small{ font-size:12px; color:var(--muted) }

    /* prevent the long list from blowing up on mobile */
    #gate-select{ width:100%; max-width:100% }
    #gate-search{ width:100% }

    /* --- sidebar toggle (base) --- */
    #side-toggle{
      position:absolute; top:8px; right:8px;
      width:28px; height:28px; border-radius:999px;
      background:var(--card); border:1px solid var(--border);
      display:flex; align-items:center; justify-content:center;
      cursor:pointer; z-index:2;
    }

    /* --- mobile (drawer) --- */
    @media (max-width:900px){
      /* hide desktop collapse button */
      #side-toggle{ display:none !important; }

      #wrap{ grid-template-columns:1fr; }
      #side{
        position:fixed; left:0; top:var(--header-h);
        bottom:0; width:min(86vw,360px);
        transform:translateX(-100%);
        transition:transform .2s ease;
        box-shadow:0 10px 24px rgba(0,0,0,.4);
        z-index:6;
      }
      body.sidebar-open #side{ transform:translateX(0); }

      #backdrop{
        position:fixed; inset:var(--header-h) 0 0 0;
        background:rgba(0,0,0,.4);
        opacity:0; pointer-events:none;
        transition:opacity .2s ease; z-index:5;
      }
      body.sidebar-open #backdrop{ opacity:1; pointer-events:auto; }

      /* show hamburger in header on mobile */
      #open-side{
        display:inline-flex !important;  /* <— beats the inline display:none */
        align-items:center;justify-content:center;
      }
    }

    /* --- desktop (collapsible rail) --- */
    @media (min-width:901px){
      /* hide mobile hamburger on desktop */
      #open-side{ display:none !important; }

      /* layout */
      #wrap{ display:flex; min-height: calc(100vh - var(--header-h,50px)); }
      #side{ width:320px; flex:0 0 auto; transition:width .18s ease; }
      #main{ flex:1 1 auto; min-width:0; }

      /* collapsed state */
      #wrap.collapsed{ --side-w:48px; }
      #wrap.collapsed #side{ width:56px; overflow:hidden; }
      #wrap.collapsed #side > *:not(#side-toggle){ display:none; } /* keep only the toggle visible */
      #wrap.collapsed #side .panel{ display:none; }

      /* IMPORTANT: keep toggle small; don't stretch full width */
      #side #side-toggle{ width:28px; height:28px; }
    }