:root {
    --blue: #1e90ff;
    --black: rgb(31, 30, 30);
    --grey: rgb(230, 226, 226);
    --white: rgb(255, 255, 255);
    --yellow: #e4f1fe;
}

body {
    font-family:'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;
    font-size: 90%;
}

main {
    padding: 1em;
    margin-left: 2em;
    margin-right: 2em;
}

a {
  color: var(--grey);
}

ul {
  padding-left: 1em;
}

.navbar {
    border-bottom: 1px solid var(--blue);
}

.navbar__title {
    color: var(--blue);
    margin-top: 0.25em;
    margin-bottom: 0.25em;
}

.navbar__subtitle {
    font-weight: 100;
    color: var(--black);
}

.container {
    padding-top: 1em;
    padding-bottom: 1em;
    font-size: 1.2em;
}

.items {
    margin-top: 1em;
    margin-bottom: 1em;
    display: flex;
    justify-content: space-around;
}

.flip-card {
    background-color: transparent;
    width: 20em;
    height: 22em;
    border: 1px solid var(--grey);
    background-color: var(--grey);
    margin: 0.5em;
}

.flip-card:nth-child(2n) {
    background-color: var(--yellow);
}
  
.flip-card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transition: transform 0.8s;
    transform-style: preserve-3d;
}
  
.flip-card:hover .flip-card-inner {
    transform: rotateY(180deg);
}
  
.flip-card-front, .flip-card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    -webkit-backface-visibility: hidden; /* Safari */
    backface-visibility: hidden;
 }
  
.flip-card-front {
    padding-top: 2.5em;
    color: var(--black);
    text-align: center;
}

.flip-card-front__image {
    width: 15em;
    height: 10em;
}

.flip-card-back {
    font-size: 0.9em;
    font-weight: 10;
    background-color: var(--blue);
    color: white;
    transform: rotateY(180deg);
}

.card-content {
  padding-left: 0.5em;
  padding-right: 0.5em;
}

@media (max-width: 768px) {
    .items {
      flex-direction: column;
      align-items: center;
      margin-left: 1em;
      margin-right: 1em;
    }

    main {
        margin-left: 0.2em;
        margin-right: 0.2em;
    }
}