html, body {
  min-height: 100%;
  margin: 0;
  padding: 0;
  font-family: Arial, sans-serif;
}

body {
  display: flex;  
  flex-direction: column;
  background-image: url("BG.jpg");
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
  background-color: #000;
  min-height: 100vh;
}

.nav a {
  color: #000000;
  text-decoration: none;
  padding: 10px;
  display: inline-block;
  transition: all 0.3s ease;
  background:linear-gradient(rgba(150, 213, 255, 0.4), rgba(150, 213, 255, 0.4));
  margin: 0;
  border-radius: 5px;
  text-align: center;
  min-width: 50px;
  margin: 5px;
}
.nav a:hover {
  background:linear-gradient(180deg, rgba(201,201,240,0.8) 0, rgba(19, 59, 133, 0.8) 20%);
  color: #ffffff;
}

.main-content a {
  color: #000000;
  text-decoration: none;
  padding: 10px;
  display: inline-block;
  transition: all 0.3s ease;
  background:linear-gradient(rgba(150, 213, 255, 0.4), rgba(150, 213, 255, 0.4));
  margin: 0;
  border-radius: 5px;
  text-align: center;
  min-width: 50px;
  margin: 5px;
}

.main-content a:hover {
  background:linear-gradient(180deg, rgba(201,201,240,0.8) 0, rgba(19, 59, 133, 0.8) 20%);
  color: #ffffff;
}

.header {
  /*background-image: linear-gradient(to bottom, rgb(120, 145, 255), rgb(68, 0, 156));*/
  border-top: 2px solid rgba(19, 59, 133, 0.8);
  border-radius: 50px 50px 0 0;
  color: #ffffff;
  padding: 10px;
  text-align: center;
  width: calc(100% - 40px);
  max-width: 90%;
  margin: 20px auto 0;
  box-sizing: border-box;
  background:linear-gradient(180deg, rgba(201,201,240,0.8) 0, rgba(19, 59, 133, 0.8) 20%);
}

.nav {
  display: flex;
  flex-wrap: wrap;
  background-color: rgba(255, 255, 255, 0.4);
  padding: 7px;
  margin: 0px auto;
  width: calc(100% - 40px);
  max-width: 90%;
  box-sizing: border-box;
  min-height: 40px;
  align-items: left, stretch;
}

.main-content {
  background-color: rgba(255, 255, 255, 0.4);
  border-radius: 0 0 20px 20px;
  padding: 20px;
  margin: 0px auto;
  width: calc(100% - 40px);
  max-width: 90%;
  box-sizing: border-box;
}

.platzhalter {flex: 1;}

.footer {
  background:linear-gradient(180deg, rgba(201,201,240,0.8) 0, rgba(19, 59, 133, 0.8) 20%);
  border-radius: 0px 50px 0 0;
  color:#ffffff;
  padding: 10px;
  text-align: center;
  width: calc(100% - 20px);
  max-width: 95%;
  margin: 10px 0px auto 0px;
  box-sizing: border-box;
  border-top: 2px solid rgba(19, 59, 133, 0.8);
  border-right: 2px solid rgba(19, 59, 133, 0.8);
  min-height: 70px;
}
.start-btn {
  position: absolute;
  left: 10px;
  transform: translateY(-50%,);
}