Some Web structures

HTML creates a list of objects on the page and makes them editable. As in the code below: Canvas and Button objects are described with conditions and characteristics.

<h1>Button with div practice</h1>

<canvas id = "d1" class="Pinkback"> </canvas>
<canvas id = "d2" class="Aquaback">  </canvas>
<input type="button" value="Change Color Pink" onclick="doPink()">
<input type="button" value="Change Color Aqua" onclick="doAqua()">

CSS exposes the graphical properties of each object and heading. The structure here resembles a class, where {} specifies useful knowledge.
When using CSS, try to rely on the extended list of parameters. I recommend W3Schools for a detailed look at function arguments.

h1 {
  color: #5F9EA0;
  font-family: courier;
}

canvas {
  width: 80pt;
  heigth: 140pt;
  padding: 5pt;
  border: 1pt solid lightgray;
  front-size: 16pt;
}

.Pinkback {
  background-color: #FAEBD7;
}

.Aquaback {
  background-color: #7FFFD4;
}

.LightGreen {
  background-color: #90EE90;
}
.Khaki {
  background-color: #F0E68C;
}

This is an example of a wider palette color description (HTML):

Last but not least, use the well-known JavaScript language. This will allow you to identify graphical models and use them in the programming structure.

function changeColor() {
  dd1=document.getElementById("d1");
  dd2=document.getElementById("d2");

  dd1.className = "GreenL";
  dd2.className = "Khaki";
}

function doPink() {
  var dd1 = document.getElementById("d1");
  dd1.style.backgroundColor = "LightGreen";

  var canvas = document.getElementById("d2");
  var ctx = canvas.getContext("2d");
  ctx.clearRect(0,0, canvas.width, canvas.height);
  //canvas.style.backgroundColor = "Khaki";
}

function doAqua() {
  var dd1 = document.getElementById("d2");
  dd1.style.backgroundColor = "Khaki";

  var ctx = dd1.getContext("2d");
  ctx.fillStyle="Brown";
  ctx.fillRect(10,10,60,60);
  ctx.fillRect(80,10,75,75);
  ctx.fillRect(165,10,90,90);

  ctx.fillStyle = "DarkSlateGray";
  ctx.font = "30px Arial";
  ctx.fillText("beaute", 20,135);
}

By the way, for concatenating three styles of describing Web pages, I recommend using CodePen at an early stage. It will help you not to get confused in this JS, HTML and CSS. Good luck!