style.css

body {
    background-color: black;
    margin: 0;
    padding: 30px;
    background-image: linear-gradient(#000000, #403042, #5c045f);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}


.container {
    position: absolute;
    display: inline-grid;
    border: solid, darkgreen;
    grid-gap: 1px;
    width: 600px;
    height: 600px;
    opacity: 1;
}


.overlay {
    position: relative;
    width: 600px;
    height: 600px;
    top: 0;
    left: 0;
    z-index: 0;
    background-image: url("sonic.png");
}

.btn_container {
    display: flex;
    flex-direction: row;
    width: 700px;
    height: 50px;
    justify-content: space-evenly;
    align-items: center;

}


#eraser {background-image: linear-gradient(to right, #c8ff00 0%, #f84600  51%, #ae00da  100%)}
#eraser {
   margin: 10px;
   padding: 15px 45px;
   text-align: center;
   text-transform: uppercase;
   transition: 0.5s;
   background-size: 200% auto;
   color: white;            
   box-shadow: 0 0 20px #eee;
   border-radius: 10px;
   display: block;
 }

 #eraser:hover {
   background-position: right center; /* change the direction of the change here */
   color: #fff;
   text-decoration: none;
 }


.input-color-container {
    position: relative;
    overflow: hidden;
    width: 40px;
    height: 40px;
    border: solid 2px #ddd;
    border-radius: 40px;
}

#colorPicker {
    position: absolute;
    right: -8px;
    top: -8px;
    width: 56px;
    height: 56px;
    border: none;
}
    
.cell {
 
    padding: 0;
    margin: 0;
    background-color: white;

}

#slidervalue {
    color:white;
}

.myslider {
    -webkit-appearance: none;
    width: 100%;
    height: 10px;
    border-radius: 5px;
    background: #eea300;
    outline: none;
    opacity: 0.7;
    -webkit-transition: .2s;
    transition: opacity .2s;
  }


.myslider::-webkit-slider-thumb {
    -webkit-appearance: none;
    height: 30px;
    width: 30px;
    background: rgb(255, 0, 43);
    border-radius: 50%;
  }

.myslider::-moz-range-thumb {
    height: 15px;
    width: 15px;
    background: pink;
    margin-top: -5px;
    border-radius: 50%;
  }