@import url('https://fonts.googleapis.com/css2?family=Source+Sans+3&display=swap');

body {
  font-family: "Source Sans 3", sans-serif;
  padding: 36px 64px;
  margin: 0;
  display: flex;
  flex-flow: column nowrap;
  align-items: center;
  color: hsl(0, 0%, 20%);
}

html::before {
  content: " ";
  display: block;
  height: 12px;
  background: linear-gradient(
    90deg,
    hsl(240, 50%, 50%) 0%,
    hsl(0, 50%, 50%) 100%
  );
}

header {
  margin-bottom: 64px;
  text-align: center;
}
header > p {
  margin-top: 0;
}

nav li {
  display: inline-block;
  margin: 0 12px;
}

h1 {
  margin: 0;
  font-size: 64px;
  margin-left: -5px;
}

h2 {
  text-align: center;
}

#profile-picture {
  float: left;
  width: 200px;
  margin-right: 24px;
  margin-bottom: 24px;
  margin-top: 6px;
  animation: shake 3s;
}

img {
  box-shadow: 2px 2px 2px hsl(0, 0%, 50%);
  border-radius: 2px;
}

p {
  margin-bottom: 36px;
  max-width: 650px;
}
p, li {
  line-height: 1.5;
  font-size: 20px;
}

.lesson-step {
  margin-bottom: 64px;
  display: flex;
}

.lesson-steps li:nth-child(even) .lesson-step {
  flex-flow: row-reverse nowrap;
}

.lesson-steps li:nth-child(odd) .lesson-step {
  flex-flow: row nowrap;
}

.lesson-steps {
  list-style: none;
  padding: 0;
}

.lesson-step img {
  width: 300px;
  margin: 0 36px;
}

@keyframes shake {
  from: {
    transform: translateY(0);
  }
  10%: {
    transform: translateY(0);
  }
  45% {
    transform: translateY(-10px);
  }
  47% {
    transform: translateY(-10px) rotateZ(-2deg);
  }
  49% {
    transform: translateY(-10px) rotateZ(2deg);
  }
  51% {
    transform: translateY(-10px) rotateZ(-2deg);
  }
  53% {
    transform: translateY(-10px) rotateZ(2deg);
  }
  56% {
    transform: translateY(-10px) rotateZ(-2deg);
  }
  59% {
    transform: translateY(-10px) rotateZ(2deg);
  }
  61% {
    transform: translateY(-10px);
  }
  to: {
    transform: translateY(0);
  }
}

.introduction, .review {
  margin: 64px auto;
  padding: 36px 0;
  border-top: 1px solid hsl(0, 0%, 70%);
  border-bottom: 1px solid hsl(0, 0%, 70%);
}

.thumbnail {
  width: 250px;
  border: 0.5px solid hsl(240, 50%, 50%);
  box-shadow: none;
}