/* Reset + base */
*{box-sizing:border-box}
html,body{margin:0;height:100%;font-family:system-ui,-apple-system,Segoe UI,Roboto,Arial}
body{background:#fafafa;color:#222}
:root{
  --green:#2e7d32; --blue:#1565c0; --red:#b71c1c; --yellow:#f9a825;
}
.app-header{position:sticky;top:0;z-index:5;display:flex;align-items:center;gap:.5rem;padding:.75rem 1rem;background:#fff;border-bottom:1px solid #eee}
.app-header h1{margin:0;font-size:1.25rem;flex:1;text-align:center}
.back-btn,.install-btn{border:none;background:#f3f3f3;padding:.5rem .75rem;border-radius:999px;cursor:pointer}
.back-btn{font-size:1.1rem}
.install-btn{font-size:1rem}
.screen{display:none;min-height:calc(100dvh - 56px);padding:1rem}
.screen.active{display:block}
.list-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:.5rem}
.fab{position:fixed;inset-inline-end:1rem;inset-block-end:1.2rem;background:#222;color:#fff;border:none;border-radius:999px;width:56px;height:56px;font-size:28px;cursor:pointer;box-shadow:0 8px 24px rgba(0,0,0,.2)}
.subjects{display:flex;flex-direction:column;gap:.6rem}
.subject-card{display:flex;align-items:center;gap:.75rem;padding:1rem;border-radius:14px;color:#fff;cursor:pointer;box-shadow:0 6px 18px rgba(0,0,0,.12)}
.subject-card .badge{background:rgba(255,255,255,.2);padding:.25rem .5rem;border-radius:999px}
.pill{display:inline-flex;align-items:center;justify-content:center;min-width:2rem;height:2rem;background:rgba(0,0,0,.08);border-radius:999px;padding:0 .5rem}
.subject-bar{display:flex;align-items:center;justify-content:space-between;gap:1rem;margin-bottom:.5rem}
.subject-title{display:flex;align-items:center;gap:.5rem}
.outline{background:#fff;border:1px solid #ddd;border-radius:10px;padding:.45rem .8rem;cursor:pointer}
.tabs{display:grid;grid-template-columns:repeat(4,1fr);gap:.5rem;margin:1rem 0}
.tab-btn{background:#f1f1f1;border:none;border-radius:10px;padding:.6rem .5rem;cursor:pointer}
.tab-pane{display:none;border-radius:12px;padding:1rem;min-height:50vh}
.tab-pane.active{display:block}
.green{background:#e8f5e9;border:1px solid #c8e6c9}
.blue{background:#e3f2fd;border:1px solid #bbdefb}
.red{background:#ffebee;border:1px solid #ffcdd2}
.yellow{background:#fff8e1;border:1px solid #ffe082}
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(120px,1fr));gap:.75rem}
.card{background:#fff;border:1px solid #eee;border-radius:12px;padding:.75rem;box-shadow:0 4px 14px rgba(0,0,0,.06)}
.note-card{height:110px;overflow:hidden;cursor:pointer}
.vlist{display:flex;flex-direction:column;gap:.6rem}
.row{display:flex;align-items:center;gap:.75rem;background:#fff;border:1px solid #eee;border-radius:12px;padding:.75rem;box-shadow:0 4px 14px rgba(0,0,0,.06);cursor:pointer}
.row .meta{flex:1}
.badge{font-size:.8rem}
.small{font-size:.85rem;color:#555}
.modal{max-width:640px;width:90vw;border:none;border-radius:16px;padding:0}
.modal::backdrop{background:rgba(0,0,0,.35)}
.form{padding:1rem;display:flex;flex-direction:column;gap:.75rem}
.form input[type=text],.form input[type=color],.form textarea,.form select,.form input[type=file]{width:100%;padding:.6rem;border:1px solid #ddd;border-radius:10px}
menu{display:flex;gap:.5rem;justify-content:flex-end;padding-top:.5rem}
button.danger{background:#c62828;color:#fff;border:none;border-radius:10px;padding:.5rem .8rem}
.img{width:100%;height:100px;border-radius:10px;object-fit:cover}
.img-viewer{position:fixed;inset:0;background:rgba(0,0,0,.85);display:none;align-items:center;justify-content:center;z-index:50}
.img-viewer img{max-width:95vw;max-height:90vh;border-radius:12px}
.hidden{display:none}
/* back button visibility */
#backBtn{visibility:hidden}
.screen:not(#screen-home) ~ .app-header #backBtn{visibility:visible}