/* === Basic selectors === */
body {
  margin: 0;
  font-family: system-ui, sans-serif;
  background: #121212;
  color: #eee;
}

/* Class + ID + attribute */
#main.container[data-theme="dark"] {
  padding: 1rem;
  border: 1px solid rgba(255, 255, 255, 0.2);
}

/* Pseudo-classes & elements */
a:hover,
a:focus-visible {
  color: hsl(210, 80%, 60%);
  text-decoration: underline;
}

input::placeholder {
  color: #999;
}

/* CSS variables */
:root {
  --accent: #4fc3f7;
  --spacing: 1rem;
}

.button {
  background: var(--accent);
  padding: calc(var(--spacing) * 1.5);
}

/* Media query */
@media (max-width: 768px) {
  .container {
    padding: 0.5rem;
  }
}

/* Keyframes */
@keyframes fade-in {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Animation usage */
.modal {
  animation: fade-in 250ms ease-out;
}

/* Complex selector */
ul > li:not(:last-child)::after {
  content: "•";
  margin-left: 0.5em;
}

/* Edge cases */
[data-value^="test"]::before {
  content: attr(data-value);
}