style.css

html {
  box-sizing: border-box;
}

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 0 auto;
  height: 100vh;
  background-image: linear-gradient(340deg, #d2d136, #991e43);
  font-family: "Andale Mono", AndaleMono, monospace;
  color: #fff;
}

div.container {
  width: 100%;
  max-width: 450px;
  padding: 1rem;
  margin: 1rem;
  border-radius: 10px;
  /*box-shadow: 2px 2px 20px 2px #d3d3d3;*/
  background-image: linear-gradient(160deg, #d2d136, #991e43);
  text-align: center;
}

p {
  text-align: left;
  line-height: 20px;
  letter-spacing: 2px;
}

input#txt,
button {
  display: block;
  width: 45%;
  min-width: 120px;
  padding: 10px;
  background: rgba(255, 255, 255, 0.5);
  /*border: 2px solid #fff;*/
  border: none;
  border-radius: 5px;
  outline: none;
  color: #fff;
}

input#txt::placeholder {
  font-size: 10px;
  color: #fff;
}

.myRange {
  -webkit-appearance: none;
  width: 100%;
  height: 15px;
  margin: 1rem 0;
  border-radius: 5px;
  background: #d3d3d3;
  outline: none;
  opacity: 0.7;
  -webkit-transition: 0.2s;
  transition: opacity 0.2s;
}

.myRange::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 25px;
  height: 25px;
  border-radius: 50%;
  background: #991e43;
  cursor: pointer;
}

.myRange::-moz-range-thumb {
  width: 25px;
  height: 25px;
  border-radius: 50%;
  background: #991e43;
  cursor: pointer;
}

div.flex-row,
div.bloc {
  display: flex;
  justify-content: space-between;
}

button.buttonRestart {
  display: block;
  width: 100%;
  min-width: 250px;
  margin-bottom: 1rem;
}