style.css

*{
  font-family: 'Roboto', sans-serif;
  background-color: #402dc0; 
  color: whitesmoke; 
}

h1{
  text-align: center;  
  font-size: 30pt;
}

canvas{
  border: 1px solid lightgray;
  width: 500px;
  height: 300px;
}

#canvasCont, #fgFileChoose, #bgFileChoose, #buttons-sliders{  
  text-align: center;
  margin: 20px;  
}

#slider-style{
  margin: 20px;    
}

#slider{
  -webkit-appearance: none;
  appearance: none;
  height: 2px;
  width: 20%;
  background-color: #494949;  
  outline: none;
  opacity: 0.5;
  -webkit-transition: .2s;
  transition: opacity .2s;
}

#slider:hover{
  opacity: 1;
}

label{
  display: inline-block;
  padding: 8px 12px; 
  cursor: pointer;
  border-radius: 4px;
  background-color: #30bb5aa2;
  font-size: 16px;
  color: #fff;
}

input[type="file"] {
  position: absolute;
  z-index: -1;
  top: 6px;
  left: 0;
  font-size: 15px;
  color: rgb(153,153,153);
}

#fgFileChoose, #bgFileChoose{
  position: relative;
}

#compositeBtn{
  background-color: #a7ff83; /* Green */
  border-radius: 6px;
  border: none;
  color: black;
  padding: 16px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  margin: 4px 2px;
  transition-duration: 0.4s;
  cursor: pointer;  
}

#clearBtn{
  background-color: #17b978; /* Green */
  border-radius: 6px;
  border: none;
  color: white;
  padding: 16px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  margin: 4px 2px;
  transition-duration: 0.4s;
  cursor: pointer;  
}

#downloadBtn{
  background-color: #086972; 
  border-radius: 6px;
  border: none;
  color: white;
  padding: 16px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  margin: 4px 2px;
  transition-duration: 0.4s;
  cursor: pointer;  
}