.topic{
  
    background-color: #2196f3; 
    text-align: center;
    font-size: 130%;
    border-bottom: 1px solid rgb(13, 17, 40);
    border-top: 1px solid rgb(13, 17, 40);
    border-right: 1px solid rgb(13, 17, 40);
    border-left: 1px solid rgb(13, 17, 40);
    margin-top: 20px;
}
.sub{
    color: #2196f3;
    background-color: rgb(13, 17, 40);
    font-size: 130%;
    text-align: center;
    border-bottom: 1px solid #2196f3 ;
    border-top: 1px solid #2196f3;
    border-right: 1px solid #2196f3;
    border-left: 1px solid #2196f3;
    margin-top: 20px;
}
.video{
  text-align: center;
}
.sidebar {
  width: 100%;
  height: 100%;
  background: rgb(13, 17, 40);
}
.sidebar header {
  font-size: 22px;
  color: #2196f3;
  line-height: 70px;
  text-align: center;
  background: rgb(13, 17, 40);
  user-select: none;
}
.sidebar ul a{
  display: block;
  height: 100%;
  width: 100%;
  line-height: 65px;
  font-size: 15px;
  color:#2196f3 ;
  padding-left: 40px;
  box-sizing: border-box;
  border-bottom: 1px solid #2196f3;
  border-top: 1px solid #2196f3;
  transition: .4s;
}
ul li:hover a{
  padding-left: 50px;
  opacity: 0.5;
}
.sidebar ul a i{
  margin-right: 16px;
}
#check{
  display: none;
}
label #btn,label #cancel{
  background: #2196f3;
  border-radius: 3px;
  cursor: pointer;
}
label #btn{
  left: 40px;
  top: 25px;
  font-size: 35px;
  color: #2196f3;
  padding: 6px 12px;
  transition: all .5s;
}
label #cancel{
  z-index: 1111;
  left: -195px;
  top: 17px;
  font-size: 30px;
  color: #2196f3;
  padding: 4px 9px;
  transition: all .5s ease;
}
#check:checked ~ .sidebar{
  left: 0;
}
#check:checked ~ label #btn{
  left: 250px;
  opacity: 0;
  pointer-events: none;
}
#check:checked ~ label #cancel{
  left: 195px;
}
#check:checked ~ section{
  margin-left: 250px;
}
section{
  background: url(bg.jpeg) no-repeat;
  background-position: center;
  background-size: cover;
  height: 100vh;
  transition: all .5s;
}
.first{
  font-size: 140%;
}