/* Ô chữ (/cong-cu/o-chu). Tệp nạp ở mọi trang → mọi lớp có tiền tố oc-. */
.chinh:has(> .oc) { max-width: 1400px; }
.oc-an-chu { position: absolute !important; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.oc-dau h1 { margin-bottom: 2px; }
.oc-soan { display: flex; flex-direction: column; gap: 14px; }
.oc-hang { display: flex; flex-wrap: wrap; gap: 10px 14px; align-items: flex-end; }
.oc-chon { flex: 1 1 260px; }
.oc-soan textarea { min-height: 220px; font-size: 1rem; line-height: 1.6; }
.oc-soan code { background: var(--c-nhat); color: var(--c-dam); padding: 1px 6px; border-radius: 6px; }
.oc-nhap { cursor: pointer; }
.oc-nhap:focus-within, #oc-nhap:focus-visible + .oc-nhap { outline: 3px solid var(--c-vien); }
#oc-bao:empty { display: none; }
#oc-bao { margin: 0; }

.oc-thanh { display: flex; flex-wrap: wrap; gap: 10px 16px; align-items: center; justify-content: space-between; }
.oc-thanh h2 { margin: 0; font-size: clamp(1.2rem, 2vw, 1.7rem); color: var(--c-dam); }
.oc-huong-dan { margin: 8px 0 4px; }
.oc-ket { min-height: 1.5em; font-weight: 700; color: var(--c-dam); margin: 4px 0 10px; }
.oc-ket--xong { color: var(--xanh-la); font-size: 1.25rem; }
.oc-khung { display: grid; gap: 20px; align-items: start; }
@media (min-width: 1000px) { .oc-khung { grid-template-columns: minmax(0, 1.5fr) minmax(300px, 1fr); } }
.oc-luoi-bao { overflow-x: auto; overflow-y: hidden; padding: 3px; }
.oc-luoi { --o: 40px; display: grid; grid-template-columns: repeat(var(--cot), var(--o)); grid-auto-rows: var(--o); width: max-content; margin: 0 auto; }
.oc-trong { background: transparent; }
.oc-o { position: relative; background: #fff; border: 1.5px solid var(--c-dam); margin: -0.75px; }
.oc-o input { width: 100%; height: 100%; border: 0; padding: 0; background: transparent; text-align: center; font: inherit;
  font-size: calc(var(--o) * .56); font-weight: 800; color: var(--chu); text-transform: uppercase; caret-color: var(--c); border-radius: 0; }
.oc-o input:focus { outline: none; }
.oc-so { position: absolute; top: 1px; left: 3px; font-size: max(9px, calc(var(--o) * .26)); font-weight: 700; line-height: 1; color: var(--phu); pointer-events: none; }
.oc-o.oc-dang { background: var(--nhan-nhat); }
.oc-o.oc-dang-o { background: #f7dc9f; box-shadow: inset 0 0 0 3px var(--c); z-index: 1; }
.oc-o.oc-dung { background: var(--xanh-la-nhat); }
.oc-o.oc-dung input { color: var(--xanh-la); }
.oc-o.oc-sai { background: var(--do-nhat); }
.oc-o.oc-sai input { color: var(--do); }
.oc-o.oc-hien input { color: var(--c); }
.oc-goi-y { display: grid; gap: 14px; }
@media (min-width: 640px) and (max-width: 999px) { .oc-goi-y { grid-template-columns: 1fr 1fr; } }
.oc-goi-y h3 { color: var(--c-dam); margin-bottom: 4px; }
.oc-goi-y ol { margin: 0; padding-left: 2em; }
.oc-goi-y li { margin-bottom: 2px; border-radius: 8px; }
.oc-goi-y li::marker { font-weight: 800; color: var(--c-dam); }
.oc-goi-y li.oc-dang { background: var(--nhan-nhat); }
.oc-cau { display: block; width: 100%; text-align: left; background: none; border: 0; padding: 6px 8px; font: inherit; color: var(--chu); cursor: pointer; border-radius: 8px; }
.oc-cau:hover { background: var(--c-nhat); }
.oc-in-dap-an { display: none; }

/* Chiếu lên lớp */
.oc-choi:fullscreen { background: var(--bg); padding: 20px clamp(16px, 3vw, 40px); overflow: auto; }
.oc-choi:fullscreen .oc-huong-dan { display: none; }
.oc-choi:fullscreen .oc-goi-y { font-size: clamp(1.05rem, 1.35vw, 1.5rem); }
.oc-choi:fullscreen .oc-khung { grid-template-columns: minmax(0, 1.5fr) minmax(320px, 1fr); }

/* In: trang 1 ô trống + gợi ý, trang 2 đáp án */
@media print {
  body:has(.oc) .dau, body:has(.oc) .chan, body:has(.oc) .demo-bar, body:has(.oc) .skip,
  .oc-dau, .oc-soan, .oc-cong-cu, .oc-huong-dan, .oc-ket { display: none !important; }
  body:has(.oc) { background: #fff; }
  .chinh:has(> .oc) { max-width: none; padding: 0; }
  .oc-choi { border: 0; box-shadow: none; padding: 0; }
  .oc-khung { display: block; }
  .oc-luoi { --o: 30px !important; margin: 12px 0 18px; }
  .oc-o input { color: transparent !important; }
  .oc-o, .oc-o.oc-dang, .oc-o.oc-dang-o, .oc-o.oc-dung, .oc-o.oc-sai { background: #fff !important; box-shadow: none !important; }
  .oc-goi-y { grid-template-columns: 1fr 1fr; font-size: 11pt; }
  .oc-goi-y li.oc-dang { background: none; }
  .oc-in-dap-an { display: block; break-before: page; }
  .oc-luoi--in .oc-o b { display: grid; place-items: center; height: 100%; font-size: 16px; color: #000; }
  .oc-ds-dap-an { columns: 2; font-size: 11pt; }
}