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

body{
  font-family:system-ui,sans-serif;
  height:100vh;
  display:flex;
  flex-direction:column;
}

.system-bar{
  display:flex;
  justify-content:space-between;
  padding:8px 14px;
  border-bottom:1px solid #ccc;
}

.layout{
  flex:1;
  display:grid;
  grid-template-columns:260px 1fr 300px;
  overflow:hidden;
}

.nav-panel,.meta-panel{
  border-right:1px solid #ddd;
  padding:10px;
  overflow:auto;
}

.viewer-panel{
  position:relative;
}

iframe{
  width:100%;
  height:100%;
  border:none;
}

ul{list-style:none}
li{
  padding:6px 8px;
  cursor:pointer;
}
li:hover{background:#eee}