/* General reset */
* {
  box-sizing: border-box;
}

/* Variables */
:root {
  --primary: #3a86ff;
  --card-bg: #e6f2ff;
}

/* Body */
body {
  font-family: 'Roboto', sans-serif;
  background-color: var(--bg, #f0f2f5);
  margin: 0;
  padding: 0;
}

/* Header */
#main-header {
  background-color: color-mix(in srgb, white 75%, #3a86ff 25%);
  text-align: center;
  padding: 10px;
  position: sticky;
  top: 0;
}

/* Cards */
.card {
  background-color: var(--card-bg, lightblue);

  /* Longhand */
  margin: 20px 30px 20px 30px;
  padding: 10px 15px 10px 15px;
  border-style: solid;
  border-color: black;
  border-width: 2px;

  /* Shorthand */
  border: 2px solid black;

  border-radius: 10px;
}

/* Headings */
.subtitle {
  color: rgb(40, 40, 40);
}

#agenda {
  background-color: hsl(45, 100%, 90%);
}

.task-box {
  background-color: hsla(140, 45%, 70%, 0.9);
}
h1, h2 {
  color: var(--primary);
}

/* Attribute selector */
[data-role="lead"] {
  font-weight: bold;
  color: orange;
}

/* Descendant */
section ul {
  color: black;
}

/* Child */
nav > ul {
  list-style: none;
  padding: 0;
}

/* Adjacent sibling */
h2 + p {
  background-color: #eef;
}

/* General sibling */
h2 ~ p {
  font-style: italic;
}

/* Hover + active */
a:hover {
  color: red;
}

button:active {
  background-color: gray;
}

/* Display */
nav li {
  display: inline-block;
  margin: 0.5em;
}

footer p {
  display: inline;
}

.subtitle {
  display: block;
}

section.card {
  width: 85%;
}

.hidden-example {
  display: none;
}

/* Text */
p {
  text-align: left;
  color: #222;
  text-decoration: none;
}

/* Flexbox */
.flex-container {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  flex-wrap: wrap;
}

.task-box {
  background-color: rgba(120, 200, 150, 0.8);
  padding: 10px;
  width: 100px;
  height: 60px;
}

/* Grid */
.grid-container {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 10px;
}

.grid-item {
  background-color: color(display-p3 0.75 0.88 1);
  padding: 1cm;
  border: 1pt solid black;
  min-width: 50mm;
  max-width: 120mm;
}

/* Position */
footer {
  position: relative;
  left: 10px;
}

/* Units */
main {
  width: 80%;
  margin: auto;
  padding: 2rem;
  font-size: 1.1em;
}

/* :has selector */
section:has(ol) {
  background-color: #fff0cc;
}

/* Nested selector */
main {
  & section {
    background-color: #f8fbff;
  }
}

/* Media query */
@media (max-width: 768px) {
  .flex-container {
    flex-direction: column;
    align-items: stretch;
  }

  .grid-container {
    grid-template-columns: 1fr;
  }

  nav li {
    display: block;
    margin: 0.4rem 0;
  }

  main {
    width: 95%;
    padding: 1rem;
  }

  body {
    font-size: 0.95rem;
  }
}