:root {
  --main-bg: #f5f5f5;
  --card-bg: white;
  --text-color: rgb(40, 40, 40);
  --heading-color: hsl(210, 70%, 30%);
  --border-color: #cfcfcf;
}

body {
  background-color: var(--main-bg, #f5f5f5);
  color: var(--text-color, #222222);
  font-family: "Nunito", Arial, sans-serif;
  font-size: 1rem;
  margin: 0;
  padding: 0;
}

header, footer {
  text-align: center;
  background-color: color-mix(in srgb, white 80%, lightblue 20%);
  padding: 1rem;
}

header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background-color: #eef3f7;
}

footer {
  position: relative;
}

main {
  background-color: var(--card-bg, white);
  width: 80%;
  max-width: 900px;
  min-width: 300px;
  margin: auto;
  padding: 20px;
  padding-top: 20px;
  border: 2px solid var(--border-color, #cfcfcf);
  border-radius: 10px;
}

h1, h2, h3 {
  color: var(--heading-color, navy);
  text-align: center;
}

h2, h3 {
  text-decoration: underline;
}

section {
  margin-top: 20px;
  margin-bottom: 20px;
  margin-left: 0;
  margin-right: 0;
  padding: 10px 15px 10px 15px;
  border-style: solid;
  border-color: #dddddd;
  border-width: 1px;
  border-radius: 8px;
  background-color: rgba(255, 255, 255, 0.9);
}

img {
  width: 100%;
  max-width: 500px;
  height: auto;
  display: block;
  margin: auto;
}

audio {
  width: 250px;
}

video {
  border: 0.2in solid #bbb;
}

a:hover {
  color: orange;
}

button:active {
  background-color: #cccccc;
}

* {
  box-sizing: border-box;
}

#attendance {
  background-color: #fefefe;
}

.card {
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.08);
  margin: 10px 20px 10px 20px;
  padding-top: 8px;
  padding-bottom: 8px;
  padding-left: 12px;
  padding-right: 12px;
  border: 2px solid #ccc;
}

section.card {
  margin: 1rem 0;
}

input[type="text"] {
  border: 1px solid #999;
}

nav ul li a {
  text-decoration: none;
}

form > fieldset {
  background-color: white;
}

h2 + p {
  color: orange;
}

h2 ~ p {
  line-height: 1.5;
}

section:has(img) {
  border-color: blue;
}

nav {
  ul {
    list-style-type: none;
  }

  li {
    display: inline-block;
    margin-right: 10px;
  }
}

/* flexbox layout */
.top-nav ul {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}

/* grid layout */
#attendance ul {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 10px;
  justify-items: center;
}

label {
  display: inline-block;
  width: 5cm;
}

summary {
  color: color(display-p3 0.2 0.4 0.8);
  display: inline;
}

.primary-btn {
  background-color: hsla(220, 70%, 55%, 0.9);
  display: inline-block;
  border: 3px solid navy;
}

span {
  color: green;
}

@media (max-width: 768px) {
  main {
    width: 95%;
    padding: 10px;
  }

  video {
    width: 100%;
    height: auto;
  }
}