* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  /*overflow-x: hidden;*/
  /* Das setzt die korrekte Darstellung auf Smartphones bei Verwendung von Bootstrap
     siehe: https://stackoverflow.com/questions/25887927/bootstrap-some-kind-of-margin-on-mobile-devices-only-right-side
     Nebenwirkung: position: sticky funktionietr nicht mehr*/
}

body {
  width: 95%;
  margin: 0 auto;
  padding-bottom: 50px;
}
@media only screen and (min-width: 1550px) {
  body {
    width: 1500px;
  }
}

.container {
  position: relative;
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
}

.navbar {
  width: 100%;
  margin: 0 auto;
  overflow: hidden;
  /* erstellt mit https://glassmorphism.com/ */
  background: rgba(120, 145, 158, 0.7);
  box-shadow: 0 4px 8px 0 rgba(31, 38, 135, 0.37);
  backdrop-filter: blur(3px);
  -webkit-backdrop-filter: blur(3px);
  border-radius: 3px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  /* Ende des extern erzeugten CSS */
  display: flex;
  justify-content: flex-start;
  align-items: center;
  color: #f2f2f2;
  z-index: 10;
}

.headerMenu {
  position: sticky;
  top: 0;
}

.footerMenu {
  width: 95%;
  position: fixed;
  bottom: 0;
}

.navbar a {
  display: block;
  font-family: Arial, Helvetica, sans-serif;
  text-align: center;
  padding: 10px 6px;
  /*text-decoration: none;*/
  font-size: 14px;
}

.navbar a:hover {
  background: #f1f1f1;
  color: black;
}

.navbar a.active {
  background-color: #4caf50;
  color: white;
}
.mainHeader {
  align-self: flex-start;
  width: 100%;
  display: flex;
  flex-direction: row;
  justify-content: space-between;
  margin: 20px 0 20px 0;
}

.mainText {
  font-family: Verdana, Geneva, Tahoma, sans-serif;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}
.mainHeadline {
  font-size: 40px;
  text-shadow: 2px 2px 5px #ccc;
  color: lightgrey;
}
.subHeadline {
  font-size: 1.5rem;
  color: darkgrey;
  margin-bottom: 0.5rem;
  font-weight: 600;
}

.defaultText {
  margin-bottom: 0.5rem;
}

.headerGraphics {
  width: 100px;
  height: 100px;
  background-color: green;
}

.multiColumn {
  -webkit-column-count: 3;
  -moz-column-count: 3;
  column-count: 3;
  -webkit-column-width: 400px;
  -moz-column-width: 400px;
  column-width: 400px;
}
.restrictedWidth {
  max-width: 900px;
}

h2,
h4 {
  text-align: center;
  margin-top: 10px;
  margin-bottom: 20px;
}

.intro-container {
  margin-top: 1rem;
  width: 100%;
  max-width: 1100px;
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: space-around;
}

.intro-column {
  font-family: Verdana, Geneva, Tahoma, sans-serif;
  width: 45%;
  min-width: 350px;
  display: flex;
  flex-direction: column;
}

/* Unterthemen */

/* Überschrift */

.topic-header {
  margin: 30px 0;
  font-family: Arial, Helvetica, sans-serif;
  text-transform: uppercase;
  font-weight: bold;
  font-size: 2em;
  letter-spacing: 0.1em;
  text-shadow: 1px 1px 3px #ccc;
  color: lightgrey;
}

/* Spektrenvorschau */

.topic {
  width: 100%;
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: space-evenly;
}

/* Einzelnes Spektrum */

.preview-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  padding: 0px;
  margin-bottom: 20px;
  width: 23%;
  border-radius: 10px;
  /*box-shadow: 10px 10px 5px silver;*/
  border: 1px solid grey;
  overflow: hidden;
  background-color: #fafafa;
}

@media only screen and (max-width: 1500px) {
  .preview-container {
    width: 30%;
  }
}

@media only screen and (max-width: 1200px) {
  .preview-container {
    width: 45%;
  }
}

@media only screen and (max-width: 800px) {
  .preview-container {
    width: 100%;
  }
}

.exercise-description {
  width: calc(100% - 20px);
  font-size: 24px;
  font-weight: bold;
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  margin-bottom: 5px;
  padding: 10px 10px 0px 10px;
  
}
.exercise-img {
  width: 100%;
  height: auto;
  aspect-ratio: 20/9;
  padding: 0px 3px 0px 3px;
}

.exercise-img img {
  max-width: 100%;
}

.exercise-navigation {
  width: 100%;
  display: flex;
  flex-direction: row;
  justify-content:space-between;
  margin: 5px 0 0 0;
  padding: 0px 10px 10px 10px;
}

.problem {
  bottom: 0;
  color: blue;
  font-weight: bold;
  font-size: 1.5rem;
  opacity: 0.8;
}
.problem:hover {
  background-color: #cccccc;
}

.problem-download {
  color: blue;
  font-weight: bold;
  font-size: 1.5rem;
  opacity: 0.8;
}

.solution {
  color: green;
  font-weight: bold;
  font-size: 1.5rem;
  opacity: 0.8;
}

.solution:hover {
  background-color: #cccccc;
}

.solution-download {
  color: green;
  font-weight: bold;
  font-size: 1.5rem;
  opacity: 0.8;
}

.PDF-preview {
  color: darkred;
  font-weight: bold;
  font-size: 1.5rem;
  opacity: 0.8;
}

a:hover,
a:visited,
a:link,
a:active {
  text-decoration: none;
  color: inherit;
}