/* Basic Reset & Layout */
body {
  font-family: 'Segoe UI', Arial, sans-serif;
  background: linear-gradient(120deg, #f0e6fa 0%, #e3f6fd 100%);
  margin: 0;
  padding: 0;
  color: #222;
}
header {
  background: #8e44ad;
  color: #fff;
  padding: 2rem 1rem 1rem 1rem;
  text-align: center;
  box-shadow: 0 2px 8px rgba(52, 152, 219, 0.08);
}
.subtitle {
  font-size: 1.2rem;
  color: #ffd200;
  margin-top: 0.5rem;
}
main {
  max-width: 800px;
  margin: 2rem auto;
  background: #fff;
  border-radius: 12px;
  box-shadow: 0 4px 24px rgba(52, 152, 219, 0.10);
  padding: 2rem 1.5rem 3rem 1.5rem;
}
.theory-section, .best-practices {
  margin-bottom: 2.5rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid #e3f6fd;
}
.theory-section h2, .demo-section h2, .best-practices h2 {
  color: #8e44ad;
}
.demo-section {
  margin-bottom: 2.5rem;
}
.demo-block {
  margin-bottom: 2rem;
  padding: 1.2rem 1rem;
  background: #f9f6ff;
  border-radius: 8px;
  box-shadow: 0 1px 4px rgba(52, 152, 219, 0.06);
}
.demo-block h3 {
  margin-top: 0;
  color: #3498db;
}
pre {
  background: #222;
  color: #ffd200;
  padding: 0.8em 1em;
  border-radius: 6px;
  overflow-x: auto;
  font-size: 0.98em;
  margin-top: 1em;
}
code {
  background: #f0e6fa;
  color: #8e44ad;
  padding: 0.1em 0.3em;
  border-radius: 4px;
  font-size: 1em;
}
/* Interactive Demos */
.demo-btn, .back-btn {
  display: inline-block;
  background: #ffd200;
  color: #8e44ad;
  padding: 0.7em 1.5em;
  border-radius: 6px;
  text-decoration: none;
  font-weight: bold;
  transition: background 0.2s, color 0.2s;
  margin-bottom: 0.5em;
  box-shadow: 0 2px 8px rgba(52, 152, 219, 0.08);
}
.demo-btn:active {
  background: #3498db;
}
 .back-btn{
  margin-top: 2rem;
 }
 .demo-btn:hover,
.demo-btn:focus,
.back-btn:hover,
.back-btn:focus {
  background: #8e44ad;
  color: #fff;
  outline: 2px solid #f7971e;
  outline-offset: 2px;
}
.child-demo {
  display: flex;
  gap: 1em;
  list-style: none;
  padding: 0;
  margin: 0.5em 0 0.5em 0;
}
.child-demo li {
  background: #e3f6fd;
  padding: 0.5em 1em;
  border-radius: 5px;
  font-weight: normal;
  color: #222;
  transition: background 0.2s, color 0.2s;
}
.child-demo li:first-child {
  color: #8e44ad;
  font-weight: bold;
}
.child-demo li:last-child {
  color: #3498db;
}
.child-demo.single li:only-child {
  background: #ffd200;
  color: #8e44ad;
  font-weight: bold;
}
.nth-demo {
  list-style: decimal inside;
  padding: 0;
  margin: 0.5em 0 0.5em 0;
}
.nth-demo li {
  background: #f0e6fa;
  margin-bottom: 0.3em;
  padding: 0.5em 1em;
  border-radius: 5px;
  transition: background 0.2s, color 0.2s;
}
.nth-demo li:nth-child(odd) {
  background: #f0e6fa;
}
.nth-demo li:nth-child(2n) {
  background: #e3f6fd;
}
.nth-demo li:nth-child(3) {
  color: #f7971e;
  font-weight: bold;
}
.nth-of-type-demo {
  display: flex;
  gap: 1em;
  list-style: none;
  padding: 0;
  margin: 0.5em 0 0.5em 0;
}
.nth-of-type-demo li {
  background: #e3f6fd;
  padding: 0.5em 1em;
  border-radius: 5px;
  color: #222;
  font-weight: normal;
  transition: background 0.2s, color 0.2s;
}
.nth-of-type-demo li:nth-of-type(2) {
  background: #ffd200;
  color: #8e44ad;
}
.nth-of-type-demo li:nth-of-type(3) {
  background: #8e44ad;
  color: #fff;
}
.empty-demo {
  display: flex;
  gap: 1em;
  margin: 0.5em 0 0.5em 0;
}
.empty-box {
  width: 100px;
  height: 2em;
  background: #e3f6fd;
  border-radius: 5px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1em;
  color: #222;
}
.empty-box:empty {
  border: 2px dashed #8e44ad;
  background: #f0e6fa;
}
.not-demo {
  display: flex;
  gap: 1em;
  list-style: none;
  padding: 0;
  margin: 0.5em 0 0.5em 0;
}
.not-demo li {
  background: #e3f6fd;
  padding: 0.5em 1em;
  border-radius: 5px;
  color: #222;
  font-weight: normal;
  transition: background 0.2s, color 0.2s;
}
.not-demo li:not(.exclude) {
  color: #3498db;
  font-weight: bold;
}
.form-demo {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7em;
  margin: 0.5em 0 0.5em 0;
  align-items: center;
}
.form-demo input[type="text"],
.form-demo input[type="email"] {
  padding: 0.5em 1em;
  border: 2px solid #e3f6fd;
  border-radius: 5px;
  font-size: 1em;
  transition: border-color 0.2s;
}
.form-demo input:required {
  border-color: #f7971e;
}
.form-demo input:valid {
  border-color: #3498db;
}
.form-demo input:invalid {
  border-color: #e74c3c;
}
.form-demo input[type="checkbox"] {
  accent-color: #8e44ad;
  margin-right: 0.3em;
}
.form-demo input:checked + label {
  color: #8e44ad;
  font-weight: bold;
}
.form-demo button {
  background: #8e44ad;
  color: #fff;
  border: none;
  border-radius: 5px;
  padding: 0.5em 1.2em;
  font-size: 1em;
  cursor: pointer;
  transition: background 0.2s;
}
.form-demo button:hover,
.form-demo button:focus {
  background: #3498db;
}
/* --- New Pseudo-Classes: :is(), :where(), :has(), :not() (advanced), :focus-visible --- */
.is-where-demo :is(h2, h3) {
  color: #8e44ad;
}
.is-where-demo p {
  background-color: #e3f6fd;
  padding: 0.3em 0.7em;
  border-radius: 4px;
}
.is-where-demo :where(p) {
  background-color:rgb(227, 246, 253);
}
.has-demo {
  display: flex;
  gap: 1em;
  margin: 0.5em 0 0.5em 0;
}
.has-demo .card {
  background-color: #fff;
  border-radius: 6px;
  padding: 0.7em 1.2em;
  box-shadow: 0 1px 4px rgba(52, 152, 219, 0.06);
  display: flex;
  align-items: center;
  gap: 0.5em;
  font-size: 1em;
  color: #222;
  border: 2px solid transparent;
  transition: border 0.2s, background 0.2s;
}
.has-demo .card:has(img) {
  border: 2px solid #ffd200;
  background: #f0e6fa;
}
.not-advanced-demo {
  display: flex;
  gap: 1em;
  list-style: none;
  padding: 0;
  margin: 0.5em 0 0.5em 0;
}
.not-advanced-demo li {
  background: #e3f6fd;
  padding: 0.5em 1em;
  border-radius: 5px;
  color: #222;
  font-weight: normal;
  transition: background 0.2s, color 0.2s;
}
.not-advanced-demo li:not(.exclude, [data-skip]) {
  color: #8e44ad;
  font-weight: bold;
}
.focus-visible-demo-btn {
  background: #ffd200;
  color: #8e44ad;
  padding: 0.7em 1.5em;
  border-radius: 6px;
  border: none;
  font-weight: bold;
  font-size: 1em;
  margin-bottom: 0.5em;
  box-shadow: 0 2px 8px rgba(52, 152, 219, 0.08);
  transition: background-color 0.2s, color 0.2s;
  outline: 1px solid transparent;
  cursor: pointer;
}
.focus-visible-demo-btn:focus-visible {
  outline: 3px solid #3498db;
  background: #e3f6fd;
}
@media (max-width: 600px) {
  main {
    padding: 1rem 0.5rem 2rem 0.5rem;
  }
  .page-header {
    padding: 1.2rem 0.5rem 0.7rem 0.5rem;
  }
  .demo-block {
    padding: 0.7rem 0.5rem;
  }
}