/* =================================================
   CORE.CSS – WEBSITE 3 NGÀY
   GLOBAL / STABLE / SCALE
================================================= */

/* ================= RESET ================= */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI",
    Roboto, Inter, Helvetica, Arial, sans-serif;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
}

/* ================= COLOR SYSTEM ================= */
:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --accent: #38bdf8;

  --text: #0f172a;
  --text-muted: #64748b;

  --bg: #ffffff;
  --bg-soft: #f8fafc;

  --white: #ffffff;
  --border: #e5e7eb;

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 18px;
}

/* ================= TYPOGRAPHY ================= */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.25;
  color: var(--text);
}

p {
  color: var(--text-muted);
}

a {
  color: var(--primary);
  text-decoration: none;
}

img {
  max-width: 100%;
  display: block;
}

/* ================= LAYOUT CORE ================= */
/* container CHỈ QUẢN LÝ CHIỀU NGANG */
.container {
  max-width: 1120px;
  margin-left: auto;
  margin-right: auto;
  padding-left: 20px;
  padding-right: 20px;
}

/* ================= DISPLAY UTIL ================= */
.flex { display: flex; }
.grid { display: grid; }

.gap-8  { gap: 8px; }
.gap-12 { gap: 12px; }
.gap-20 { gap: 20px; }
.gap-32 { gap: 32px; }

/* ================= BUTTON CORE ================= */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 22px;
  border-radius: 999px;
  font-weight: 600;
  cursor: pointer;
  transition: all .25s ease;
  border: none;
}

.btn-primary {
  background: var(--primary);
  color: var(--white);
}

.btn-primary:hover {
  background: var(--primary-dark);
  transform: translateY(-1px);
}

.btn-outline {
  background: transparent;
  border: 2px solid var(--primary);
  color: var(--primary);
}

.btn-outline:hover {
  background: var(--primary);
  color: var(--white);
}

/* ================= FORM CORE ================= */
input,
textarea,
select {
  width: 100%;
  padding: 12px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  font-family: inherit;
  font-size: 1rem;
}

input:focus,
textarea:focus {
  outline: none;
  border-color: var(--primary);
}

/* ================= CARD CORE ================= */
.card {
  background: var(--white);
  border-radius: var(--radius-lg);
  border: 1px solid rgba(15,23,42,.06);
}

/* ================= UTILITIES ================= */
.text-center { text-align: center; }
.hidden { display: none !important; }

.mt-20 { margin-top: 20px; }
.mt-40 { margin-top: 40px; }
.mb-20 { margin-bottom: 20px; }
.mb-40 { margin-bottom: 40px; }

/* ================= MOBILE SAFE ================= */
@media (max-width: 768px) {
  .container {
    padding-left: 16px;
    padding-right: 16px;
  }
}