header{
    height: 200px;
    background-color: grey;
}
#menu{
    height: 800px;
    width: 20%;
    background-color: #eeeeee;
    float: left;
}
#content{
    height: 800px;
    width: 80%;
    background-color: rgb(150, 147, 110);
    float: left;
}
#content > div {padding-left: 15px;}
footer{
    height: 100px;
    clear: both;
    background-color: lightgreen;
}


.button-89 {
  --b: 3px;   /* border thickness */
  --s: .45em; /* size of the corner */
  --color: #373B44;
  
  padding: calc(.5em + var(--s)) calc(.9em + var(--s));
  color: var(--color);
  --_p: var(--s);
  background:
    conic-gradient(from 90deg at var(--b) var(--b),#0000 90deg,var(--color) 0)
    var(--_p) var(--_p)/calc(100% - var(--b) - 2*var(--_p)) calc(100% - var(--b) - 2*var(--_p));
  transition: .3s linear, color 0s, background-color 0s;
  outline: var(--b) solid #0000;
  outline-offset: .6em;
  font-size: 16px;

  border: 0;

  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
  border-radius: 4px;
  margin: 20px;
}

/* CSS */
.button-90 {
  color: #fff;
  padding: 15px 25px;
  border-radius: 100px;
  background-color: #4C43CD;
  background-image: radial-gradient(93% 87% at 87% 89%, rgba(0, 0, 0, 0.23) 0%, transparent 86.18%), radial-gradient(66% 87% at 26% 20%, rgba(255, 255, 255, 0.41) 0%, rgba(255, 255, 255, 0) 69.79%, rgba(255, 255, 255, 0) 100%);
  box-shadow: 2px 19px 31px rgba(0, 0, 0, 0.2);
  font-weight: bold;
  font-size: 16px;
width: 80%;
margin-bottom: 20px;
margin-left: 20px;
  border: 0;

  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;

  cursor: pointer;
}
div{
  font-family: cursive;
}