:root{--navy:#062b59;--blue:#0967c9;--orange:#ff8a00;--soft:#f4f7fa;--line:#dbe7f4;--muted:#62738a}
*{box-sizing:border-box}
body{margin:0;color:#14233a;font-family:Inter,"Segoe UI",Arial,sans-serif;background:var(--soft)}
a{color:inherit;text-decoration:none}
button,select,textarea{font:inherit}
.wrap{width:min(1160px,calc(100% - 30px));margin:auto}
.top{background:#fff;border-bottom:1px solid var(--line)}
.nav{height:70px;display:flex;align-items:center;gap:14px}
.brand{margin-right:auto;color:var(--navy);font-weight:900}
.nav .zalo{padding:9px 12px;color:#fff;font-size:13px;font-weight:800;background:var(--blue);border-radius:6px}
.breadcrumb{padding:18px 0 0;color:var(--muted);font-size:13px}
.breadcrumb a{color:var(--blue)}
.grid{display:grid;grid-template-columns:1fr .9fr;gap:18px;padding:18px 0 52px}
.panel{padding:24px;background:#fff;border:1px solid var(--line);border-radius:14px}
.panel h1{margin:0 0 12px;color:var(--navy);font-size:34px;line-height:1.2}
.meta{display:flex;flex-wrap:wrap;gap:10px}
.meta span{padding:6px 9px;color:#38516d;font-size:12px;background:#edf5ff;border-radius:999px}
.problemText{color:#35465e;line-height:1.65}
.problemText h2{margin:25px 0 7px;color:var(--navy);font-size:20px}
.sample{padding:15px;color:#dceaff;font-family:Consolas,monospace;white-space:pre-wrap;background:#081b38;border-radius:8px}
.editor{overflow:hidden;margin-top:14px;background:#07182f;border-radius:10px}
.toolbar{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:10px 13px;color:#dceaff;background:#102849}
.toolbar select{padding:6px 8px;color:#dceaff;background:#17385f;border:1px solid #31577f;border-radius:6px}
.saved{font-size:11px;color:#8fb0d4}
.editor textarea{width:100%;min-height:360px;padding:17px;color:#e4ecf8;font:14px/1.55 Consolas,monospace;resize:vertical;background:#07182f;border:0;outline:0}
.actions{display:flex;flex-wrap:wrap;justify-content:flex-end;gap:8px;margin-top:12px}
.btn{padding:11px 15px;color:#fff;font-weight:800;cursor:pointer;background:var(--blue);border:0;border-radius:7px}
.btn.secondary{color:var(--navy);background:#edf5ff}
.btn.submit{background:var(--orange)}
.msg{display:none;margin-top:12px;padding:12px;color:#72550c;background:#fff8e8;border-radius:8px}
.navProblems{display:flex;justify-content:space-between;margin-top:20px}
.navProblems a{color:var(--blue);font-size:13px;font-weight:800}
.seoNote{margin-top:20px;padding:15px;color:#4c6077;font-size:13px;line-height:1.6;background:#f7faff;border-left:3px solid var(--blue)}
@media(max-width:850px){.grid{grid-template-columns:1fr}.panel{padding:19px}.editor textarea{min-height:300px}.nav{height:62px}.panel h1{font-size:28px}}