/* Giao diện gốc (khung ChatGPT) — phần 1/8. Nạp đúng thứ tự trong HTML (file sau ghi đè file trước). */
:root {
  --navy: #252b77;
  --deep: #151b50;
  --orange: #ef5e2f;
  --ink: #17243d;
  --muted: #6e778b;
  --line: #e3e7ee;
  --paper: #f5f7fb;
  --radius: 18px;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  font:
    15px/1.65 'Segoe UI',
    Arial,
    sans-serif;
  color: var(--ink);
  background: #fff;
}
a {
  color: inherit;
  text-decoration: none;
}
button,
input,
select,
textarea {
  font: inherit;
}
button,
a,
input,
select,
textarea {
  -webkit-tap-highlight-color: transparent;
}
button {
  cursor: pointer;
}
button:disabled {
  cursor: wait;
  opacity: 0.6;
}
a,
button {
  touch-action: manipulation;
}
button:focus-visible,
a:focus-visible {
  outline: 3px solid #ef5e2f;
  outline-offset: 4px;
}
input:focus,
select:focus,
textarea:focus {
  outline: 2px solid #444da3;
  outline-offset: 1px;
}
h1,
h2,
h3,
p {
  margin-top: 0;
}
h1,
h2,
h3 {
  line-height: 1.2;
  letter-spacing: -0.035em;
}
h1 {
  font-size: clamp(38px, 4.5vw, 64px);
  font-weight: 750;
  margin-bottom: 24px;
}
h2 {
  font-size: clamp(28px, 3vw, 40px);
  margin-bottom: 20px;
}
h3 {
  font-size: 21px;
}
p {
  margin-bottom: 18px;
}
.container {
  width: min(1180px, calc(100% - 64px));
  margin: auto;
}
.topbar {
  background: var(--deep);
  color: #e5e6f2;
  font-size: 11px;
  letter-spacing: 0.04em;
}
.topbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  min-height: 34px;
}
.demo-tag {
  opacity: 0.8;
}
header {
  background: white;
  border-bottom: 1px solid var(--line);
  position: relative;
  z-index: 5;
}
.nav {
  min-height: 92px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 26px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 800;
  font-size: 22px;
  line-height: 1.15;
}
.brand img {
  width: 163px;
  height: 60px;
  object-fit: contain;
}
.brand small {
  display: block;
  font-size: 10px;
  letter-spacing: 4px;
  margin-top: 5px;
}
.brandmark {
  background: var(--orange);
  color: #fff;
  border-radius: 10px;
  padding: 6px 10px;
}
.brandmark span {
  font-size: 15px;
}
nav {
  display: flex;
  gap: 27px;
}
nav a {
  font-size: 13px;
  font-weight: 600;
  padding: 34px 0;
  position: relative;
  white-space: nowrap;
}
nav a.active {
  color: var(--orange);
}
nav a.active:after {
  content: '';
  position: absolute;
  bottom: 21px;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--orange);
}
.button {
  border: 0;
  background: var(--orange);
  color: #fff;
  border-radius: 8px;
  display: inline-flex;
  gap: 24px;
  justify-content: center;
  align-items: center;
  padding: 14px 22px;
  font-weight: 650;
  font-size: 14px;
  line-height: 1.5;
  transition:
    background 0.15s,
    transform 0.15s;
}
.button:hover {
  background: #d84a20;
  transform: translateY(-1px);
}
.button.small {
  font-size: 12px;
  padding: 12px 18px;
}
.button.navy {
  background: var(--navy);
}
.button.outline {
  background: transparent;
  border: 1px solid var(--line);
  color: var(--ink);
}
.button.light {
  background: white;
  color: var(--navy);
}
.menu-button {
  display: none;
}
.hero {
  background: var(--deep);
  color: white;
  position: relative;
  overflow: hidden;
  padding: 66px 0 110px;
}
.hero:after {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(ellipse at 90% 20%, #45488b55, transparent 55%);
  pointer-events: none;
}