/* ============================================================
   Bài Tập — giao diện tối ưu cho iPad (cảm ứng + Apple Pencil)
   ============================================================ */

:root{
  --bg:#f4f1ea;
  --panel:#ffffff;
  --ink:#22303a;
  --muted:#6b7a85;
  --line:#dfd9cd;
  --brand:#1f7a6b;
  --brand-soft:#e3f3ef;
  --brand-dark:#155a4f;
  --accent:#e4572e;
  --accent-soft:#fdece6;
  --ok:#188a4a;
  --ok-soft:#e2f5ea;
  --bad:#d0342c;
  --bad-soft:#fdeaea;
  --warn:#c98a00;
  --shadow:0 1px 2px rgba(30,40,50,.06), 0 8px 24px rgba(30,40,50,.08);
  --shadow-lg:0 10px 40px rgba(30,40,50,.18);
  --r:14px;
  --tap:46px;
  --safe-b:env(safe-area-inset-bottom,0px);
  --safe-t:env(safe-area-inset-top,0px);
  --font:"SF Pro Text",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
}

*{box-sizing:border-box}
html,body{height:100%}
html{-webkit-text-size-adjust:100%}
body{
  margin:0; font-family:var(--font); color:var(--ink); background:var(--bg);
  -webkit-font-smoothing:antialiased; overscroll-behavior:none;
}
button{font:inherit;color:inherit}
input{font:inherit}
.app{min-height:100%;display:flex;flex-direction:column}

/* ---------- nút chung ---------- */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:8px;
  min-height:var(--tap); padding:0 18px; border-radius:12px;
  border:1px solid var(--line); background:var(--panel); color:var(--ink);
  font-weight:600; font-size:16px; cursor:pointer; text-decoration:none;
  -webkit-tap-highlight-color:transparent; touch-action:manipulation;
  transition:transform .08s ease, background .15s ease, border-color .15s ease;
}
.btn:active{transform:scale(.97)}
.btn.primary{background:var(--brand);border-color:var(--brand);color:#fff}
.btn.accent{background:var(--accent);border-color:var(--accent);color:#fff}
.btn.ghost{background:transparent;border-color:transparent}
.btn.small{min-height:38px;padding:0 12px;font-size:14px;border-radius:10px}
.btn.danger{color:var(--bad);border-color:#f0cfcd}
.btn:disabled{opacity:.5;cursor:default}
.icon{font-size:19px;line-height:1}

.chip{display:inline-flex;align-items:center;gap:6px;padding:4px 10px;border-radius:999px;
  background:var(--brand-soft);color:var(--brand-dark);font-size:13px;font-weight:600}
.chip.gray{background:#eceae4;color:var(--muted)}
.chip.ok{background:var(--ok-soft);color:var(--ok)}
.chip.bad{background:var(--bad-soft);color:var(--bad)}

.hidden{display:none !important}

/* ---------- thanh trên cùng ---------- */
.topbar{
  position:sticky;top:0;z-index:40;display:flex;align-items:center;gap:12px;
  padding:calc(10px + var(--safe-t)) 16px 10px; background:rgba(255,255,255,.86);
  backdrop-filter:saturate(1.6) blur(14px); -webkit-backdrop-filter:saturate(1.6) blur(14px);
  border-bottom:1px solid var(--line);
}
.topbar h1{font-size:18px;margin:0;font-weight:700;letter-spacing:-.01em}
.topbar .sub{font-size:12.5px;color:var(--muted);margin-top:1px}
.topbar .grow{flex:1;min-width:0}
.topbar .titlewrap{min-width:0}
.topbar .titlewrap h1{overflow:hidden;text-overflow:ellipsis;white-space:nowrap}

/* ---------- thư viện ---------- */
.wrap{max-width:1100px;margin:0 auto;padding:20px 16px 60px;width:100%}
.hero{background:linear-gradient(135deg,#1f7a6b,#2f9c78);color:#fff;border-radius:20px;
  padding:26px 24px;box-shadow:var(--shadow);margin-bottom:22px}
.hero h2{margin:0 0 8px;font-size:24px;letter-spacing:-.02em}
.hero p{margin:0 0 18px;opacity:.92;font-size:15px;line-height:1.5;max-width:60ch}
.hero .btn{background:#fff;border-color:#fff;color:var(--brand-dark)}
.hero .btn.ghost2{background:rgba(255,255,255,.16);border-color:rgba(255,255,255,.4);color:#fff}
.hero-actions{display:flex;gap:10px;flex-wrap:wrap}

.section-title{display:flex;align-items:baseline;gap:10px;margin:26px 0 12px}
.section-title h3{margin:0;font-size:17px}
.section-title span{color:var(--muted);font-size:13.5px}

.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:16px}
.card{background:var(--panel);border:1px solid var(--line);border-radius:var(--r);
  overflow:hidden;box-shadow:var(--shadow);display:flex;flex-direction:column}
.card .thumb{aspect-ratio:1/1.28;background:#f7f5f0;border-bottom:1px solid var(--line);
  display:flex;align-items:center;justify-content:center;overflow:hidden}
.card .thumb img{width:100%;height:100%;object-fit:cover;object-position:top center}
.card .thumb .ph{font-size:44px;opacity:.3}
.card .body{padding:14px 14px 6px;flex:1}
.card .body h4{margin:0 0 4px;font-size:15.5px;line-height:1.35}
.card .body p{margin:0;color:var(--muted);font-size:13px;line-height:1.45}
.card .meta{display:flex;gap:6px;flex-wrap:wrap;margin-top:10px}
.card .actions{display:flex;gap:8px;padding:12px 14px}
.card .actions .btn{flex:1}

.empty{text-align:center;padding:44px 20px;color:var(--muted);border:1.5px dashed var(--line);
  border-radius:var(--r);background:#fbfaf7}
.empty .big{font-size:40px;margin-bottom:10px}

/* ---------- toast ---------- */
.toasts{position:fixed;left:0;right:0;bottom:calc(18px + var(--safe-b));z-index:200;
  display:flex;flex-direction:column;align-items:center;gap:8px;pointer-events:none}
.toast{background:#22303a;color:#fff;padding:11px 18px;border-radius:12px;font-size:14.5px;
  box-shadow:var(--shadow-lg);animation:pop .2s ease}
.toast.bad{background:var(--bad)}
.toast.ok{background:var(--ok)}
@keyframes pop{from{opacity:0;transform:translateY(8px)}}

/* ---------- modal ---------- */
.modal-bg{position:fixed;inset:0;background:rgba(20,28,34,.45);z-index:150;display:flex;
  align-items:center;justify-content:center;padding:20px;animation:fade .15s ease}
@keyframes fade{from{opacity:0}}
.modal{background:var(--panel);border-radius:18px;max-width:520px;width:100%;
  box-shadow:var(--shadow-lg);max-height:88vh;display:flex;flex-direction:column}
.modal.wide{max-width:760px}
.modal header{padding:18px 20px 0}
.modal header h3{margin:0;font-size:19px}
.modal .content{padding:14px 20px;overflow:auto}
.modal footer{padding:14px 20px calc(16px + var(--safe-b));display:flex;gap:10px;justify-content:flex-end;
  border-top:1px solid var(--line);flex-wrap:wrap}

.field{margin-bottom:14px}
.field label{display:block;font-size:13px;font-weight:600;color:var(--muted);margin-bottom:5px}
.field input[type=text],.field input[type=number],.field textarea,.field select{
  width:100%;min-height:var(--tap);padding:10px 12px;border:1px solid var(--line);
  border-radius:10px;background:#fff;font-size:16px}
.field textarea{min-height:76px;resize:vertical;line-height:1.45}
.field .hint{font-size:12.5px;color:var(--muted);margin-top:5px;line-height:1.45}
.row{display:flex;gap:12px}
.row>*{flex:1}

/* ============================================================
   TRÌNH LÀM BÀI
   ============================================================ */
.player{display:flex;flex-direction:column;height:100dvh;overflow:hidden}
.player .topbar{flex:0 0 auto}
.player-main{flex:1;display:flex;min-height:0}

/* thanh công cụ */
.tools{
  flex:0 0 auto;display:flex;flex-direction:column;gap:6px;padding:10px 8px;
  background:var(--panel);border-right:1px solid var(--line);overflow-y:auto;
  width:74px;align-items:center;
}
.tool{
  width:56px;height:52px;border-radius:12px;border:1px solid transparent;background:transparent;
  display:flex;flex-direction:column;align-items:center;justify-content:center;gap:2px;
  cursor:pointer;-webkit-tap-highlight-color:transparent;touch-action:manipulation;color:var(--ink);
}
.tool span.ic{font-size:21px;line-height:1}
.tool span.lb{font-size:10.5px;color:var(--muted);font-weight:600}
.tool.on{background:var(--brand-soft);border-color:#bfe3da}
.tool.on span.lb{color:var(--brand-dark)}
.tool:active{transform:scale(.94)}
.tool:disabled{opacity:.35}
.tool-sep{width:40px;height:1px;background:var(--line);margin:4px 0}
.tool .ic.letter{font-family:Arial,Helvetica,sans-serif;font-weight:800;font-size:20px}
.tool .swatch-ic{width:24px;height:24px;border-radius:50%;border:2px solid #fff;
  box-shadow:0 0 0 1.5px var(--line);background:#1a44d6}
.szdot{background:var(--ink);border-radius:50%;display:block}

/* bảng chọn nhỏ (màu & nét, menu Thêm) */
.popover{position:fixed;z-index:130;background:var(--panel);border:1px solid var(--line);
  border-radius:16px;padding:12px;box-shadow:var(--shadow-lg);animation:pop .15s ease;max-width:min(300px,92vw)}
.pop-title{font-size:12px;font-weight:700;color:var(--muted);margin:2px 2px 8px}
.pop-title:not(:first-child){margin-top:14px}
.pop-colors{display:grid;grid-template-columns:repeat(3,44px);gap:10px}
.pop-sw{width:44px;height:44px;border-radius:50%;border:3px solid #fff;
  box-shadow:0 0 0 1.5px var(--line);cursor:pointer;padding:0;touch-action:manipulation}
.pop-sw.on{box-shadow:0 0 0 3px var(--brand)}
.pop-sizes{display:flex;gap:10px}
.pop-sz{flex:1;min-width:44px;height:44px;border-radius:12px;border:1.5px solid var(--line);
  background:#fbfaf7;display:flex;align-items:center;justify-content:center;cursor:pointer;
  padding:0;touch-action:manipulation;color:var(--ink)}
.pop-sz.on{border-color:var(--brand);background:var(--brand-soft)}
.pop-menu{display:flex;flex-direction:column;gap:2px;min-width:212px}
.pop-item{display:flex;align-items:center;gap:11px;width:100%;min-height:46px;padding:0 10px;
  border:0;background:none;border-radius:10px;font-size:15px;cursor:pointer;text-align:left;
  touch-action:manipulation;color:var(--ink)}
.pop-item:hover{background:var(--brand-soft)}
.pop-item .pi{font-size:18px;width:24px;text-align:center;flex:0 0 auto}

/* vùng trang */
.pages-scroll{flex:1;overflow:auto;-webkit-overflow-scrolling:touch;background:#e9e5dc;
  padding:16px 12px calc(120px + var(--safe-b));display:flex;flex-direction:column;align-items:stretch;gap:18px}
.page{position:relative;background:#fff;box-shadow:var(--shadow);border-radius:6px;overflow:hidden;
  flex:0 0 auto;line-height:0;container-type:inline-size;margin:0 auto}
.page>img{display:block;width:100%;height:auto;user-select:none;-webkit-user-drag:none;pointer-events:none}
.page .ink{position:absolute;inset:0;width:100%;height:100%;touch-action:none}
.page .ink.off{pointer-events:none;touch-action:auto}
.page .layer{position:absolute;inset:0}
.page .layer.off{pointer-events:none}
.page-num{position:absolute;left:8px;top:8px;background:rgba(34,48,58,.6);color:#fff;
  font-size:11px;padding:2px 8px;border-radius:999px;line-height:1.6;z-index:2}
/* ---------- ô gõ chữ ---------- */
.txtlayer{position:absolute;inset:0}
.txtlayer.off{pointer-events:none}
.txtlayer.off .txtbox .tb-grip,
.txtlayer.off .txtbox .tb-del,
.txtlayer.off .txtbox .tb-wide{display:none}
.txtlayer.off .txtbox textarea{border-color:transparent;background:transparent}

.txtbox{position:absolute}
.txtbox textarea{
  display:block;width:100%;min-height:1.4em;margin:0;padding:2px 4px;resize:none;overflow:hidden;
  border:1.5px dashed rgba(31,122,107,.45);border-radius:6px;background:rgba(255,255,255,.72);
  outline:none;font-weight:600;-webkit-tap-highlight-color:transparent;
}
.txtbox textarea::placeholder{color:#a9b6bd;font-weight:500}
.txtbox.on textarea{border-style:solid;border-color:var(--brand);background:#fff;
  box-shadow:0 0 0 3px rgba(31,122,107,.15)}
.txtbox .tb-grip,.txtbox .tb-del,.txtbox .tb-wide{
  position:absolute;border:1px solid var(--line);background:#fff;border-radius:50%;
  width:24px;height:24px;display:flex;align-items:center;justify-content:center;
  font-size:12px;line-height:1;cursor:pointer;padding:0;box-shadow:0 1px 3px rgba(30,40,50,.18);
  touch-action:none;-webkit-tap-highlight-color:transparent;color:var(--muted);
}
.txtbox .tb-grip{left:-13px;top:-13px;cursor:move}
.txtbox .tb-del{right:-13px;top:-13px;color:var(--bad)}
.txtbox .tb-wide{right:-13px;bottom:-11px;width:20px;height:20px;cursor:ew-resize;
  background:var(--brand);border-color:var(--brand)}

/* ---------- màn hẹp / dọc ---------- */
@media (max-width:700px){
  .player-main{flex-direction:column}
  .tools{flex-direction:row;width:auto;order:2;border-right:none;border-top:1px solid var(--line);
    overflow-x:auto;padding:6px 8px;gap:4px}
  .tool{width:52px;height:48px;flex:0 0 auto}
  .tool-sep{width:1px;height:32px;margin:0 3px}
  .pages-scroll{padding-bottom:24px}
  .playbar{position:static;flex:0 0 auto}
}
@media print{.topbar,.tools,.playbar{display:none!important}}