:root {
  --gray: #ddd;
  --white: #fdfdfd;
  --blue: hsla(199, 82%, 52%, 1);
  --blue-bkg: hsla(199, 82%, 70%, 0.35);
  --blue-font: hsla(199, 82%, 35%, 1);
}

html {
  box-sizing: border-box;
  font-size: 1em;
}

*,
*::before,
*::after {
  box-sizing: inherit;
}

body {
  border: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Ubuntu,
    Oxygen, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  -webkit-font-kerning: auto;
          font-kerning: auto;
  -moz-osx-font-smoothing: grayscale;
  -webkit-font-smoothin: antialised;
  font-weight: 300;
  height: 100vh;
  -webkit-hyphens: auto;
      -ms-hyphens: auto;
          hyphens: auto;
  line-height: 1.5;
  margin: 0;
  overflow-wrap: break-word;
  padding: 0;
  text-rendering: optimizeLegibility;
}
.container {
  align-content: center;
  display: grid;
  height: 100%;
  width: 100%;
  justify-content: center;
}

.lesson {
  align-items: center;
  width: 15rem;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.btn {
  background-color: var(--white);
  border: 2px solid var(--gray);
  border-bottom: 5px solid var(--gray);
  border-radius: 9px;
  font-size: 1rem;
  padding: 0.25rem 0.35rem;
  margin: 0.2rem;
}

.selected {
  background-color: var(--blue-bkg);
  border-color: var(--blue);
  color: var(--blue-font);
}

.btn:focus,
.btn:active {
  -webkit-animation: pick 0.15s ease-in;
          animation: pick 0.15s ease-in;
}

@-webkit-keyframes pick {
  100% {
    border-bottom-width: 2px;
    border-bottom-style: solid;
  }
}

@keyframes pick {
  100% {
    border-bottom-width: 2px;
    border-bottom-style: solid;
  }
}