* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body { 
  background-image: url("https://i.ibb.co/Lg0X5Qp/music028.gif");
  min-height: 100vh;
  max-width: 100%;
}

header {
  background-image: url("https://i.ibb.co/1L40JgX/write001.jpg");
  background-color: violet;
  border: 0.25rem rgb(100, 100, 100) solid;
  
  width: 50%;
  height: 4rem;
  
  margin: 1.5rem auto;
  padding: 0.75rem;
  
  text-align: center;
  font-family: "Courier New", monospace;
}

h1 {
  margin: 0;
}

#flex {
  display: flex;
  margin: 1.5rem auto;
  width: 80%;
  height: 20rem;
}

main {
  height: 100%;
  width: 70%;
  order: 2;
  margin: 0 1rem;
  padding: 1rem;
  
  background-color: red;
  background-image: url("https://i.ibb.co/1G9Lkxv/paper013.gif");
  border: #2780F5 solid 0.3rem;
  
  text-indent: 1.5rem;
  
  overflow: scroll;
}

main h2 {
  margin: 1.5rem 0 0.5rem 0;
}

main ul {
  padding-left: 2rem;
  list-style-position: inside;
}

aside {
  height: 100%;
  width: 30%;
  order: 1;
  margin: 0 1rem;
  padding: 1rem 0;
  
  background-image: url("https://i.ibb.co/44pS3jn/blue198.gif");
  border: #095CC8 solid 0.3rem;
}

aside button {
  display: block;
  width: 100%;
  height: 25%;
  
  outline: none;
  border: none;
  
  color: black;
  font-weight: 700;
  background-color: rgba(100, 100, 100, 0.6);
  
  cursor: pointer;
  transition: 0.3s;
}

aside button:hover {
  background-color: darkgrey;
}

aside button.active {
  color: red;
  background-color: slategray;
}