* {
  margin:0; 
  font: 12px 'verdana'; 
  line-height:1.4;
  box-sizing: border-box;
}

body {
  display: flex; 
  flex-direction: column;
  min-height: calc(100vh - 40px);
  Margin: 20px;
  border: 1px solid black;
  border-radius: 24px;
  box-shadow: 8px 8px 8px rgba(0, 0, 0, 0.3);
}

body > div {
  flex-grow: 1;
  display: flex; 
}

/*----- Header -----*/
header{
  display: flex;
  height: 36px;
  border-radius: 24px 24px 0 0;
  background-color: #6699CC;
  color:white;
  display: flex; 
}

header span {
  width: 100px;
  border-left: 4px solid silver;
  padding: 1px 8px;
  font-size: 14px; 
  text-align: center;
  line-height: 32px;
/*  text-shadow: 1px 1px 1px #888, 2px 2px 2px #666; */
}

Header span:first-child {
  flex-grow: 1;
  text-align: center;
  border-left: 0;
  border-radius: 24px 0 0 0;
  font-size: 20px; 
/*  font-style: italic; */
  padding: 1px 8px;
  text-align: center;
  text-shadow: 1px 1px 1px #888, 2px 2px 2px #666;
  background-color: #FF0000 /* #E85A4F #FF6347 #FF5733 #C23B22  */
}

Header span:not(:first-child):hover {
  background-color: #5786B6; /* #5786B6 #7DAADF #688FA8  */
}

/*----- Footer -----*/
footer {
  display: flex;
  height: 24px;
  background-color: #6699CC;
  border-radius: 0 0 24px 24px;
  color:white
}

footer span {
  border-left: 1px inset #86B9EC;
  font-size: 14px; 
  font-style: italic; 
  padding: 1px 8px;
  text-align: center;
  text-shadow: 1px 1px 1px #888, 2px 2px 2px #666;
}

footer span:first-child {
  border-left: 0;
  flex-grow: 1;
  text-align: left;
}

/*----- Center -----*/
body > div {
  flex-grow: 1;
  display: flex; 
}

nav {
  width: 200px;
  background-color: #CCC;
  overflow: auto;
}

main {
  flex-grow: 1;
  border-left: 2px solid #AAA;
  overflow: auto;
  position: relative;
}

#ifMain {
  border: none;
  width: 100%;
  height: 100%;
}
/*----- Menu -----*/
nav > div {
/*  display: none;  */
}

nav > div > h3 {
  height: 36px;
  line-height: 36px;
  color:white;
  font-size: 18px;
  background-color: #6699CC;
  text-align: center;
}

ul {
  list-style-type:none;
  padding-left: 8px;
  margin: 2px;
}

li {
  height: 48px;
  margin: 8px;
  padding: 8px;
  border-right : 3px solid #AAA;
  border-bottom: 3px solid #AAA;
  background-color: #EEE;
  font-size: 16px;
}