/* ==========================================================================
   BASE STYLES & RESET — VỊ NHÀ MÌNH
   Responsive: mobile (≤640px), tablet (641–1024px), desktop (≥1025px)
   ========================================================================== */

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  overflow-x: hidden;
}

body {
  font-family: var(--font-family);
  background-color: var(--color-bg);
  color: var(--color-text-main);
  line-height: 1.6;
  min-height: 100vh;
  min-height: 100dvh;
  overflow-x: hidden;
  transition: background-color var(--transition-normal), color var(--transition-normal);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, svg, picture {
  display: block;
  max-width: 100%;
  height: auto;
}

input, button, textarea, select {
  font: inherit;
  color: inherit;
}

button {
  cursor: pointer;
  border: none;
  background: none;
}

a {
  color: inherit;
  text-decoration: none;
}

ul, ol {
  list-style: none;
}

/* Layout Container */
.container {
  width: 100%;
  max-width: var(--container-max-width);
  margin-left: auto;
  margin-right: auto;
  padding-left: var(--space-4);
  padding-right: var(--space-4);
}

/* Responsive Grid System (Rubric Tiêu chí 3: Mobile, Tablet, Desktop) */
/* Desktop (>= 1025px) */
@media (min-width: 1025px) {
  .container {
    padding-left: var(--space-6);
    padding-right: var(--space-6);
  }
}

/* Tablet (641px - 1024px) */
@media (max-width: 1024px) and (min-width: 641px) {
  .container {
    padding-left: var(--space-5);
    padding-right: var(--space-5);
  }
}

/* Mobile (<= 640px) */
@media (max-width: 640px) {
  .container {
    padding-left: var(--space-4);
    padding-right: var(--space-4);
  }
}

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

h1 { font-size: clamp(1.8rem, 4vw, 2.75rem); letter-spacing: -0.02em; }
h2 { font-size: clamp(1.4rem, 3vw, 2rem); letter-spacing: -0.01em; }
h3 { font-size: clamp(1.15rem, 2vw, 1.4rem); }
h4 { font-size: 1.1rem; }

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

/* Tối ưu hóa cảm ứng cho Mobile & Mac (iOS Safari, Android Chrome) */
button, a, input, select, textarea {
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}

/* Vùng chạm cảm ứng tối thiểu 44x44px (WCAG 2.5.5 / 2.5.8) */
button,
.btn,
.btn-icon,
input:not([type="checkbox"]):not([type="radio"]),
select,
textarea {
  min-height: 44px;
}

.btn-icon,
button.btn-icon {
  min-width: 44px;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

@media (max-width: 768px) {
  body {
    padding-bottom: 74px; /* Tránh bị che bởi thanh điều hướng dưới */
  }
}

/* ==========================================================================
   MOTION & ANIMATION TIÊU CHUẨN (T27)
   - Chỉ animate transform và opacity (GPU accelerated).
   - Tuyệt đối không transition: all.
   - Hỗ trợ prefers-reduced-motion cho người dùng nhạy cảm tiền đình.
   - Hỗ trợ hover: hover cho thiết bị dùng chuột, chống dính hover trên cảm ứng.
   ========================================================================== */

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

@media (hover: hover) and (pointer: fine) {
  .btn:hover:not(:disabled) {
    transform: translateY(-2px);
  }
  .card:hover {
    transform: translateY(-2px);
  }
}

/* ==========================================================================
   ACCESSIBILITY (WCAG 2.1 AA — T30)
   ========================================================================== */

/* Trạng thái :focus-visible tương phản cao (WCAG 2.4.7) */
:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

button:focus-visible,
.btn:focus-visible,
a:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* Skip link cho bàn phím & Screen Reader (WCAG 2.4.1) */
.skip-link {
  position: absolute;
  left: -9999px;
  top: var(--space-2);
  padding: 10px 16px;
  background: var(--color-primary);
  color: #ffffff !important;
  font-weight: 700;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  z-index: 10000;
  box-shadow: var(--shadow-lg);
  text-decoration: none;
}

.skip-link:focus,
.skip-link:focus-visible {
  left: var(--space-4);
  top: var(--space-4);
  outline: 3px solid var(--color-accent);
  outline-offset: 2px;
}