:root{
  --bg:#05051a;
  --fg:#d6f4e6;
  --dim:#8a9aa2;
  --green:#5eff84;
  --cyan:#7df9ff;
  --blue:#5e9bff;
  --red:#ff5e7a;
  --line:rgba(126,249,255,.22);
}
*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;color:var(--fg);background:var(--bg);
  font-family:ui-monospace,"JetBrains Mono",Menlo,Consolas,monospace;
  overflow-x:hidden;display:grid;place-items:center;position:relative;
  min-height:100vh;
}

/* aurora blobs */
.aurora{position:fixed;inset:0;overflow:hidden;z-index:0;pointer-events:none}
.aurora i{position:absolute;border-radius:50%;filter:blur(100px);opacity:.5}
.b1{width:620px;height:620px;left:-180px;top:-200px;
    background:radial-gradient(circle,var(--green),transparent 70%);
    animation:f1 22s ease-in-out infinite}
.b2{width:720px;height:720px;right:-200px;top:-160px;
    background:radial-gradient(circle,var(--cyan),transparent 70%);
    animation:f2 28s ease-in-out infinite}
.b3{width:540px;height:540px;left:30%;bottom:-260px;
    background:radial-gradient(circle,var(--blue),transparent 70%);
    animation:f3 32s ease-in-out infinite}
@keyframes f1{50%{transform:translate(40px,80px)}}
@keyframes f2{50%{transform:translate(-60px,50px)}}
@keyframes f3{50%{transform:translate(20px,-60px)}}

/* grid overlay */
body::before{
  content:"";position:fixed;inset:0;pointer-events:none;z-index:1;
  background-image:
    linear-gradient(rgba(94,255,132,.06) 1px,transparent 1px),
    linear-gradient(90deg,rgba(126,249,255,.06) 1px,transparent 1px);
  background-size:48px 48px;
  mask-image:radial-gradient(ellipse at center,#000 30%,transparent 75%);
  -webkit-mask-image:radial-gradient(ellipse at center,#000 30%,transparent 75%);
}

/* frame */
.frame{
  position:relative;z-index:2;
  width:min(560px,92vw);
  padding:32px 30px 26px;
  background:rgba(8,12,28,.7);
  border:1px solid var(--line);
  border-radius:2px;
  box-shadow:
    0 0 0 1px rgba(126,249,255,.10),
    0 0 40px rgba(94,255,132,.20),
    0 0 80px rgba(126,249,255,.14);
  clip-path:polygon(0 0,calc(100% - 18px) 0,100% 18px,100% 100%,18px 100%,0 calc(100% - 18px));
}

.header{
  display:flex;justify-content:space-between;align-items:center;
  border-bottom:1px solid var(--line);
  padding-bottom:12px;margin-bottom:18px;
}
.brand{
  font-size:13px;letter-spacing:.4em;text-transform:uppercase;
  color:var(--cyan);
  text-shadow:0 0 8px var(--cyan),0 0 18px rgba(126,249,255,.6);
}
.brand b{
  color:var(--green);
  text-shadow:0 0 8px var(--green),0 0 18px rgba(94,255,132,.6);
}
/* language switcher — 2 flag buttons trong header */
.lang-switch{display:flex;gap:6px}
.flag-btn{
  display:inline-flex;align-items:center;gap:6px;
  padding:6px 10px;
  background:transparent;
  border:1px solid var(--line);
  color:var(--dim);
  font:600 11px/1 inherit;letter-spacing:.2em;text-transform:uppercase;
  cursor:pointer;
  transition:border-color .15s, color .15s, opacity .15s, filter .15s;
  opacity:.55;
  filter:grayscale(60%);
}
.flag-btn .flag{font-size:14px;line-height:1;filter:none}
.flag-btn:hover{opacity:1;filter:none}
.flag-btn.is-active{
  border-color:var(--green);
  color:var(--green);
  text-shadow:0 0 6px rgba(94,255,132,.6);
  opacity:1;
  filter:none;
  cursor:default;
}
.flag-btn:focus-visible{outline:2px solid var(--cyan);outline-offset:2px}
.flag-btn.is-active:focus-visible{outline-color:var(--green)}

.label{
  display:block;
  font-size:11px;letter-spacing:.3em;text-transform:uppercase;
  color:var(--green);
  text-shadow:0 0 6px rgba(94,255,132,.55);
  margin-bottom:8px;
}
.input{
  display:block;width:100%;
  background:rgba(126,249,255,.03);
  border:1px solid var(--cyan);
  color:var(--cyan);
  padding:14px 16px;
  font:14px/1 inherit;
  letter-spacing:.18em;
  box-shadow:
    inset 0 0 12px rgba(126,249,255,.12),
    0 0 14px rgba(126,249,255,.2);
  text-shadow:0 0 6px rgba(126,249,255,.6);
  outline:none;
  transition:border-color .15s, box-shadow .15s;
}
.input::placeholder{color:rgba(126,249,255,.35)}
.input:focus{border-color:var(--green);box-shadow:inset 0 0 12px rgba(94,255,132,.15),0 0 18px rgba(94,255,132,.3)}
.input.is-invalid{
  border-color:var(--red);
  color:var(--red);
  text-shadow:0 0 6px rgba(255,94,122,.6);
  box-shadow:inset 0 0 12px rgba(255,94,122,.15),0 0 14px rgba(255,94,122,.3);
}

.code-wrap{
  margin:24px 0 8px;
  padding:22px 16px;
  border:1px dashed rgba(94,255,132,.45);
  background:linear-gradient(180deg,rgba(94,255,132,.06),rgba(126,249,255,.04));
  position:relative;text-align:center;
  transition:border-color .15s, background .15s;
}
.code-wrap::before,.code-wrap::after{
  content:"";position:absolute;width:14px;height:14px;
  border:1px solid var(--green);
}
.code-wrap::before{top:-1px;left:-1px;border-right:0;border-bottom:0}
.code-wrap::after{bottom:-1px;right:-1px;border-left:0;border-top:0}
.code-wrap.is-error{border-color:rgba(255,94,122,.6)}
.code-wrap.is-error::before,.code-wrap.is-error::after{border-color:var(--red)}

.code{
  font-size:60px;letter-spacing:.18em;line-height:1;
  color:var(--cyan);
  text-shadow:
    0 0 6px var(--cyan),
    0 0 18px var(--cyan),
    0 0 36px rgba(126,249,255,.7),
    0 0 60px rgba(94,255,132,.4);
  font-weight:700;
  transition:opacity .2s;
}
.code.is-flash{opacity:.4}
.code.is-error{
  color:var(--red);
  text-shadow:0 0 6px var(--red),0 0 18px rgba(255,94,122,.7);
}
.code.is-placeholder{color:var(--dim);text-shadow:none}
.code .gap{display:inline-block;width:.5em}

.code-meta{
  margin-top:10px;font-size:11px;letter-spacing:.25em;text-transform:uppercase;
  color:var(--dim);
}

.bar{
  margin:18px 0 16px;
  display:flex;align-items:center;gap:14px;
  font-size:12px;letter-spacing:.2em;
}
.bar .num{
  color:var(--green);
  text-shadow:0 0 6px rgba(94,255,132,.7);
  font-variant-numeric:tabular-nums;
  min-width:60px;
}
.track{
  flex:1;height:6px;background:rgba(126,249,255,.08);
  border:1px solid var(--line);position:relative;overflow:hidden;
}
.fill{
  position:absolute;inset:0;width:100%;
  background:linear-gradient(90deg,var(--green),var(--cyan));
  box-shadow:0 0 12px var(--cyan);
  transform-origin:left center;
  transition:transform .1s linear;
}

.actions{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin-top:14px}
.btn{
  padding:12px 10px;background:transparent;
  border:1px solid var(--cyan);color:var(--cyan);
  font:600 11px/1 inherit;letter-spacing:.3em;text-transform:uppercase;
  text-shadow:0 0 6px rgba(126,249,255,.6);
  box-shadow:inset 0 0 10px rgba(126,249,255,.1),0 0 10px rgba(126,249,255,.15);
  cursor:pointer;transition:all .15s;
}
.btn:hover:not(:disabled){background:rgba(126,249,255,.08)}
.btn:disabled{opacity:.4;cursor:not-allowed}
.btn:focus-visible{outline:2px solid var(--cyan);outline-offset:3px}
.btn.pri{
  border-color:var(--green);color:var(--green);
  text-shadow:0 0 6px rgba(94,255,132,.6);
  box-shadow:inset 0 0 10px rgba(94,255,132,.12),0 0 14px rgba(94,255,132,.3);
}
.btn.pri:focus-visible{outline-color:var(--green)}

.footer{
  margin-top:18px;padding-top:12px;border-top:1px dashed var(--line);
  display:flex;justify-content:space-between;
  color:var(--dim);font-size:10px;letter-spacing:.2em;text-transform:uppercase;
}

/* responsive */
@media (max-width: 480px){
  .frame{padding:24px 18px 18px;width:96vw}
  .code{font-size:44px}
  .actions{gap:8px}
  .brand{font-size:11px;letter-spacing:.3em}
  .flag-btn{padding:5px 8px;letter-spacing:.15em}
}

/* a11y: tôn trọng prefers-reduced-motion — tắt aurora, blink, flash, transitions dài */
@media (prefers-reduced-motion: reduce){
  *,*::before,*::after{
    animation-duration:.01ms !important;
    animation-iteration-count:1 !important;
    transition-duration:.01ms !important;
  }
}