/* ===== Hungdiffusion.com — shared tokens & chrome (dark mặc định) ===== */
:root {
  --bg: radial-gradient(130% 110% at 82% -12%, #211F45 0%, #131228 46%, #0C0B1D 100%);
  --surface: rgba(255, 255, 255, .09);
  --surface2: #2B2966;
  --ink: #FFFFFF;
  --muted: #E4E3F7;
  --faint: #C0BFE4;
  --border: rgba(255, 255, 255, .1);
  --border2: rgba(255, 255, 255, .22);
  --accent: #5858E6;
  --accent2: #5858E6;
  --accent-strong: #9B9BF2;
  --accent-soft: rgba(88, 88, 230, .14);
  --accent-line: rgba(88, 88, 230, .42);
  --on-accent: #FFFFFF;
  --card: #FFFFFF;
  --card-ink: #2B2A55;
  --card-muted: #55547E;
  --chrome: rgba(17, 16, 36, .92);
  --footer-card: #12111F;
  --blob-o: 1;
  --chip: #232250;
  --frame: linear-gradient(175deg, rgba(255, 255, 255, .05) 0%, rgba(255, 255, 255, .05) 100%);
}

:root[data-theme="light"] {
  --bg: linear-gradient(170deg, #ECEEFF 0%, #F6F7FF 38%, #FFFFFF 62%, #EFECFF 100%);
  --surface: rgba(88, 88, 230, .07);
  --surface2: #EBECFA;
  --ink: #1C1B3A;
  --muted: #3C3B6B;
  --faint: #6D6C9C;
  --border: rgba(28, 27, 58, .14);
  --border2: rgba(28, 27, 58, .24);
  --accent-strong: #4646D0;
  --accent-soft: rgba(88, 88, 230, .1);
  --accent-line: rgba(88, 88, 230, .38);
  --chrome: rgba(255, 255, 255, .93);
  --footer-card: #FFFFFF;
  --blob-o: .22;
  --chip: #E4E5F7;
  --frame: linear-gradient(175deg, rgba(88, 88, 230, .07) 0%, rgba(88, 88, 230, .07) 100%);
}

* { box-sizing: border-box; }

html { background: var(--bg); }

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  font-family: 'Be Vietnam Pro', system-ui, sans-serif;
}

a { color: var(--accent-strong); text-decoration: none; }
a:hover { color: #BCBCF8; }
:root[data-theme="light"] a:hover { color: #4646D0; }

.mono { font-family: 'IBM Plex Mono', monospace; }
.ic { width: 18px; height: 18px; flex: none; }

@keyframes tlUp {
  from { opacity: 0; transform: translateY(18px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes tlIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

/* ===== Header ===== */
.hd-nav {
  animation: tlIn .5s ease 0s both;
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 72px;
  padding: 12px 48px;
  border-bottom: 1px solid var(--border);
  background: var(--chrome);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}
.hd-nav .brand { display: flex; align-items: center; color: var(--ink); }
.hd-nav .brand img { height: 36px; width: auto; display: block; }
:root[data-theme="light"] .hd-nav .brand img { filter: invert(1) hue-rotate(180deg) saturate(1.15); }

.hd-nav .nav-right { display: flex; align-items: center; gap: 28px; margin-left: auto; }
.hd-nav .nav-links {
  display: flex;
  align-items: center;
  gap: 32px;
  font-size: 14.5px;
  font-weight: 500;
}
.hd-nav .nav-links a { color: var(--muted); }
.hd-nav .nav-links a:hover { color: var(--accent-strong); }
.hd-nav .nav-links a.active { color: var(--accent-strong); font-weight: 600; }

.theme-toggle {
  position: relative;
  width: 54px;
  height: 28px;
  border-radius: 999px;
  background: var(--surface2);
  border: 1px solid var(--border2);
  cursor: pointer;
  user-select: none;
  flex: none;
  padding: 0;
  transition: border-color .2s ease;
}
.theme-toggle:hover { border-color: var(--accent); }
.theme-toggle .knob {
  position: absolute;
  top: 3px;
  left: 4px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: left .3s cubic-bezier(.22, 1, .36, 1);
}
:root[data-theme="light"] .theme-toggle .knob { left: 29px; }
.theme-toggle .knob svg { width: 11px; height: 11px; }
.theme-toggle .knob .sun-ic { display: none; }
:root[data-theme="light"] .theme-toggle .knob .sun-ic { display: block; }
:root[data-theme="light"] .theme-toggle .knob .moon-ic { display: none; }

.nav-menu-btn {
  display: none;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  width: 30px;
  height: 30px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0;
  flex: none;
}
.nav-menu-btn span {
  display: block;
  width: 24px;
  height: 1.5px;
  border-radius: 2px;
  background: var(--ink);
  transition: transform .2s ease, opacity .2s ease;
}
.hd-nav.open .nav-menu-btn span:nth-child(1) { transform: translateY(7.5px) rotate(45deg); }
.hd-nav.open .nav-menu-btn span:nth-child(2) { opacity: 0; }
.hd-nav.open .nav-menu-btn span:nth-child(3) { transform: translateY(-7.5px) rotate(-45deg); }

@media (max-width: 860px) {
  .hd-nav { padding: 10px 20px; min-height: 60px; }
  .hd-nav .nav-right { gap: 12px; }
  .nav-menu-btn { display: inline-flex; }
  .hd-nav .nav-links {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    z-index: 50;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    background: var(--chrome);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border);
    box-shadow: 0 16px 32px rgba(0, 0, 0, .18);
    padding: 8px 0;
  }
  .hd-nav.open .nav-links { display: flex; }
  .hd-nav .nav-links a { padding: 14px 24px; font-size: 15.5px; }
  .hd-nav .nav-links a.active { background: var(--accent-soft); }
}

/* ===== Form đăng ký khoá học (popup) ===== */
.reg-overlay {
  position: fixed;
  inset: 0;
  z-index: 200;
  display: none;
  align-items: flex-start;
  justify-content: center;
  overflow-y: auto;
  background: rgba(10, 9, 25, .62);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  padding: 48px 20px;
}
.reg-overlay.open { display: flex; }
.reg-modal {
  background: #FFFFFF;
  color: #1C1B3A;
  border-radius: 24px;
  padding: 52px 56px;
  max-width: 880px;
  width: 100%;
  animation: tlUp .4s cubic-bezier(.22, 1, .36, 1) both;
}
.reg-modal h2 {
  margin: 0 0 14px;
  font-size: 34px;
  font-weight: 800;
  letter-spacing: -.02em;
  color: #111;
}
.reg-modal h2::after {
  content: "";
  display: block;
  width: 120px;
  height: 4px;
  border-radius: 2px;
  background: #FC4F4F;
  margin-top: 14px;
}
.reg-modal .reg-note { margin: 0 0 8px; font-size: 16px; font-style: italic; line-height: 1.65; color: #26253E; }
.reg-modal .reg-note a { color: #6B6BE8; }
.reg-modal .reg-note.small { font-size: 15px; }
.reg-form { display: flex; flex-direction: column; gap: 14px; margin-top: 14px; }
.reg-form select,
.reg-form input,
.reg-form textarea {
  font-family: 'Be Vietnam Pro', system-ui, sans-serif;
  font-size: 15.5px;
  color: #1C1B3A;
  background: #FAFAFB;
  border: 1px solid #D8D8E2;
  border-radius: 8px;
  padding: 13px 16px;
  width: 100%;
  outline: none;
  transition: border-color .15s ease;
  appearance: auto;
}
.reg-form select:focus,
.reg-form input:focus,
.reg-form textarea:focus { border-color: #5858E6; }
.reg-form input::placeholder,
.reg-form textarea::placeholder { color: #9C9BB5; }
.reg-form textarea { min-height: 150px; resize: vertical; line-height: 1.6; }
.reg-submit {
  align-self: flex-start;
  font-family: 'Be Vietnam Pro', system-ui, sans-serif;
  font-size: 15px;
  font-weight: 700;
  letter-spacing: .04em;
  color: #fff;
  background: #7678EA;
  border: none;
  border-radius: 8px;
  padding: 13px 26px;
  cursor: pointer;
}
.reg-submit:hover { background: #5858E6; }
.reg-submit:disabled { opacity: .6; cursor: default; }
.reg-status { margin: 0; font-size: 14.5px; font-weight: 600; }
.reg-status.success { color: #17934C; }
.reg-status.error { color: #D64545; }
.reg-status.error a { color: #5858E6; }

@media (max-width: 860px) {
  .reg-overlay { padding: 20px 12px; }
  .reg-modal { padding: 28px 22px; border-radius: 18px; }
  .reg-modal h2 { font-size: 24px; }
}