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

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background-color: #fff;
  color: #111;
  margin: 0;
  padding: 0;
  line-height: 1.5;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

a {
  color: #0366d6;
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 24px;
  border-bottom: 1px solid #e1e4e8;
  background-color: #fff;
  position: sticky;
  top: 0;
  z-index: 10;
}

header .logo {
  display: flex;
  align-items: center;
  font-weight: 600;
  font-size: 1.5rem;
  color: #24292e;
  gap: 10px;
  -webkit-user-select: none;
  user-select: none;
}

header .logo img {
  height: 36px;
  width: 36px;
  border-radius: 8px;
  object-fit: contain;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.button {
  appearance: none;
  border: none;
  background: none;
  color: #0f1923;
  cursor: pointer;
  position: relative;
  padding: 8px 16px;
  text-transform: uppercase;
  font-weight: bold;
  font-size: 14px;
  transition: all .15s ease;
  white-space: nowrap;
  display: flex;
  align-items: center;
}

.button::before,
.button::after {
  content: '';
  display: block;
  position: absolute;
  right: 0;
  left: 0;
  height: calc(50% - 5px);
  border: 1px solid #7D8082;
  transition: all .15s ease;
}

.button::before {
  top: 0;
  border-bottom-width: 0;
}

.button::after {
  bottom: 0;
  border-top-width: 0;
}

.button:active,
.button:focus {
  outline: none;
}

.button:active::before,
.button:active::after {
  right: 3px;
  left: 3px;
}

.button:active::before {
  top: 3px;
}

.button:active::after {
  bottom: 3px;
}

.button_lg {
  position: relative;
  display: block;
  padding: 10px 20px;
  color: #fff;
  background-color: #0f1923;
  overflow: hidden;
  box-shadow: inset 0px 0px 0px 1px transparent;
  border-radius: 6px;
}

.button_lg::before {
  content: '';
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  width: 2px;
  height: 2px;
  background-color: #0f1923;
}

.button_lg::after {
  content: '';
  display: block;
  position: absolute;
  right: 0;
  bottom: 0;
  width: 4px;
  height: 4px;
  background-color: #0f1923;
  transition: all .2s ease;
}

.button_sl {
  display: block;
  position: absolute;
  top: 0;
  bottom: -1px;
  left: -8px;
  width: 0;
  background-color: #ff4655;
  transform: skew(-15deg);
  transition: all .2s ease;
  border-radius: 6px;
}

.button_text {
  position: relative;
  padding: 0 8px;
}

.button:hover {
  color: #0f1923;
}

.button:hover .button_sl {
  width: calc(100% + 15px);
}

.button:hover .button_lg::after {
  background-color: #fff;
}

.btn-secondary {
  padding: 10px 18px;
  border: 1px solid #d1d5da;
  border-radius: 6px;
  font-weight: 600;
  color: #24292e;
  background-color: #fafbfc;
  cursor: pointer;
  transition: background-color 0.3s ease, border-color 0.3s ease;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.9rem;
  white-space: nowrap;
}

.btn-secondary:hover {
  background-color: #f3f4f6;
  border-color: #a2a9b1;
}

#lang-select {
  padding: 6px 12px;
  font-size: 0.9rem;
  border-radius: 6px;
  border: 1px solid #d1d5da;
  background-color: #fafbfc;
  color: #24292e;
  cursor: pointer;
  -webkit-user-select: none;
  user-select: none;
  white-space: nowrap;
}

main {
  max-width: 960px;
  margin: 40px auto;
  padding: 0 24px;
  flex-grow: 1;
}

main h1 {
  font-size: 2.8rem;
  font-weight: 700;
  margin-bottom: 10px;
  color: #24292e;
}

main p.subtitle {
  font-size: 1.3rem;
  color: #586069;
  margin-bottom: 36px;
  font-weight: 600;
}

/* Bố cục 4 tính năng cùng hàng */
.feature-grid {
  display: flex;
  gap: 32px;
  margin-bottom: 50px;
  justify-content: space-between;
  flex-wrap: wrap;
}

.feature-item {
  flex: 1 1 22%;
  min-width: 200px;
  padding-bottom: 0;
  border-bottom: none;
}

.feature-item strong {
  font-weight: 700;
  display: block;
  margin-bottom: 8px;
  font-size: 1.1rem;
  color: #24292e;
}

.feature-item p {
  margin: 0;
  color: #586069;
  font-size: 0.95rem;
  line-height: 1.4;
}

.article {
  border-top: 1px solid #e1e4e8;
  padding-top: 32px;
  max-width: 800px;
  margin: 0 auto 80px;
  color: #24292e;
  font-size: 1rem;
  line-height: 1.5;
}

.article time {
  float: right;
  font-size: 0.9rem;
  color: #6a737d;
  font-weight: 500;
}

.article h2 {
  font-size: 1.9rem;
  font-weight: 700;
  margin-bottom: 12px;
  border-bottom: 1px solid #e1e4e8;
  padding-bottom: 6px;
}

.article p strong {
  font-weight: 700;
}

.article p code {
  background-color: #f6f8fa;
  color: #c7254e;
  font-family: monospace;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.95rem;
}

.article ol {
  padding-left: 20px;
  margin-bottom: 1em;
}

.article ol li {
  margin-bottom: 0.8em;
  font-weight: 600;
}

footer {
  border-top: 1px solid #e1e4e8;
  padding: 20px 24px;
  text-align: center;
  color: #586069;
  font-size: 0.9rem;
  -webkit-user-select: none;
  user-select: none;
}

@media (max-width: 1024px) {
  .feature-grid {
    flex-wrap: wrap;
    gap: 24px;
  }

  .feature-item {
    min-width: 180px;
  }
}

@media (max-width: 800px) {
  .feature-grid {
    flex-direction: column;
    gap: 12px;
  }

  .feature-item {
    min-width: unset;
    flex: 1 1 100%;
  }
}

@media (max-width: 720px) {
  header {
    flex-wrap: wrap;
    justify-content: center;
    gap: 12px;
  }

  main {
    margin: 24px auto;
    padding: 0 16px;
  }

  .header-actions {
    justify-content: center;
    width: 100%;
  }

  .button,
  .btn-secondary,
  #lang-select {
    width: 100%;
    text-align: center;
  }

  .feature-grid {
    flex-direction: column;
    gap: 12px;
  }

  .feature-item {
    flex: 1 1 100%;
    min-width: unset;
  }
}

.demo-gallery {
  max-width: 900px;
  margin: 32px auto 0 auto;
  padding: 0 16px 32px 16px;
}

.gif-row {
  display: flex;
  gap: 20px;
  justify-content: center;
  flex-wrap: wrap;
}

.gif-row img {
  width: 240px;
  max-width: 100%;
  border-radius: 12px;
  box-shadow: 0 3px 16px rgba(0, 0, 0, 0.07);
  background: #f7f7f7;
  transition: transform 0.2s;
}

.gif-row img:hover {
  transform: scale(1.045) rotate(-1.5deg);
}

@media (max-width: 800px) {
  .gif-row {
    flex-direction: column;
    align-items: center;
    gap: 16px;
  }

  .gif-row img {
    width: 90%;
  }
}

.demo-gallery h2 {
  text-align: center;
  font-size: 1.2rem;
  margin-bottom: 20px;
  color: #24292e;
}