style.css

#main {
  width: 80%;
  margin: auto;
}

.options {
  /*height: 10vh;*/
  width: 100%;
  margin: auto;
  margin-top: 2vh;
  margin-bottom: 5vh;
  padding: 2vh;
  border-style: solid;
  border-width: thin;
  border-color: #CCCCCC;
  background-color: #F4F4F4;
  display:flex;
  flex-wrap: wrap;
  align-items:center;
  justify-content:center;
}

label {
  font-family: Arial, Helvetica, sans-serif;
  font-size: 24px;
  margin: 1vh;
}

#note {
  height: 35vh;
  width: 100%;
  padding: 2vh;
  margin: auto;
  border-style: solid;
  border-width: thin;
  border-color: #CCCCCC;
  background-color: #F4F4F4;
  display:flex;
  align-items:center;
  justify-content:center;
  font-size: 20vh
}

h1, h3 {
  font-family: Arial, Helvetica, sans-serif;
}

.break {
  flex-basis: 100%;
  height: 0;
}

#durationText {
}

.startbutton {
  background-color: #4CAF50; /* Green */
  border: none;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 24px;
}

.stopbutton {
  background-color: #DC143C; /* Green */
  border: none;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 24px;
}

.startbutton:active, .stopbutton:active {
  font-weight: bold;
}

button::before {
  display: block;
  content: attr(title);
  font-weight: bold;
  height: 0;
  overflow: hidden;
  visibility: hidden;
}

.slider {
  -webkit-appearance: none;  /* Override default CSS styles */
  appearance: none;
  width: 75%; /* Full-width */
  height: 25px; /* Specified height */
  background: #03254C; /* Grey background */
  outline: none; /* Remove outline */
  opacity: 0.7; /* Set transparency (for mouse-over effects on hover) */
  -webkit-transition: .2s; /* 0.2 seconds transition on hover */
  transition: opacity .2s;
}

/* Mouse-over effects */
.slider:hover {
  opacity: 1; /* Fully shown on mouse-over */
}

/* The slider handle (use -webkit- (Chrome, Opera, Safari, Edge) and -moz- (Firefox) to override default look) */
.slider::-webkit-slider-thumb {
  -webkit-appearance: none; /* Override default look */
  appearance: none;
  width: 25px; /* Set a specific slider handle width */
  height: 25px; /* Slider handle height */
  background: #FFFFFF; /* Green background */
  cursor: pointer; /* Cursor on hover */
}

.slider::-moz-range-thumb {
  width: 25px; /* Set a specific slider handle width */
  height: 25px; /* Slider handle height */
  background: #FFFFFF; /* Green background */
  cursor: pointer; /* Cursor on hover */
}