js-game/styles.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  outline: none;
}

body {
  width: 100%;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px;
  overflow: hidden;
  background: linear-gradient(#CB356B, #BD3F32);
}

.app {
  background: #fff;
  padding: 20px;
  width: 600px;
  margin: 0 auto;
  box-shadow: 0 1px 30px 0 rgba(0,0,0,0.14), 0 0px 0px 0 rgba(0,0,0,.12), 0 0px 0px 0px rgba(0,0,0,.3);
  border-radius: 10px;
}

.app__header {
  padding: 20px;
  text-align: center;
}

.app__content {
  display: flex;
  position: relative;
  align-items: center;
  justify-content: center;
}

.app__footer {
  padding: 20px;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.input {
  display: flex;
  flex-direction: column;
  margin-bottom: 10px;
}

.input label {
  display: inline-block;
  max-width: 100%;
  margin-bottom: 3px;
  color: #acacac;
  font-family: GothamPro,sans-serif;
  font-size: .8rem;
  font-weight: normal;
  line-height: 1.2rem;
}

.input input {
  display: block;
  width: 100%;
  max-height: 2.8rem;
  padding: .8rem 1rem;
  font-size: inherit;
  font-family: inherit;
  font-weight: inherit;
  line-height: 1.4;
  color: #000;
  background: #fff none;
  border: 1px solid #999;
  border-radius: 5px;
}

.game {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid #ccc;
  background: #ccc;
  min-height: 300px;
  min-width: 300px;
  max-width: 300px;
  max-height: 300px;
}

.hide {
  display: none!important;
}

.btn {
  position: absolute;
  z-index: 1;
  display: inline-block;
  padding: 1rem 2.3rem;
  margin-bottom: 0;
  font-weight: normal;
  font-family: GothamPro, sans-serif;
  font-size: 1rem;
  line-height: 1.3rem;
  text-align: center;
  white-space: nowrap;
  vertical-align: middle;
  touch-action: manipulation;
  cursor: pointer;
  user-select: none;
  background: #fad64e;
  color: #3f3f3f;
  border: none;
  border-radius: 2.8rem;
  transition: transform .2s ease-in-out,box-shadow .2s ease-in-out,-webkit-transform .2s ease-in-out,-webkit-box-shadow .2s ease-in-out;
  will-change: transform;
}

.btn:disabled {
  background: #ccc!important;
  border: 1px solid #ccc;
  color: #000;
  cursor: not-allowed;
}

.btn:active {
  transition: transform .1s ease-in-out,box-shadow .1s ease-in-out!important;
  transform: none!important;
  box-shadow: none!important;
}

.btn:hover {
  box-shadow: 0 6px 16px 0 rgba(0,0,0,.2);
  transform: translateY(-1px);
}