Changing text size and backgrounds

CSS is the way to do this.

Work through the tutorials here: https://www.w3schools.com/css/ while not as comprehensive as some would like, the basic information is presented well and gives you the opportunity to learn by doing, right in the site itself.

Once you have a basic understanding of how CSS works within HTML, you can do pretty much anything you want to modify the look of your page.

Style your site with CSS code.  See screenshot and code example below.

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>CSS Grids - Vertical Centering</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<style>
body, html {
margin: 0;
height: 100%;
display: grid;
background: #333 url(https://placeimg.com/1200/900/nature) no-repeat center center;
background-size: cover;
}
.container {
padding: 2%;
width: 80%;
text-align: center;
margin: auto;
background-color: rgba(0,0,0,0.5);
color: #FFF;
}
/* Special Rules for Tablets & Higher */
@media only screen and (min-width: 500px){
h1 {font-size:5vw}
h2 {font-size:4vw}
h3 {font-size:3vw}
 p {font-size:2vw}
}
</style>
</head>
<body>
<div class="container">
<h1>Welcome to CSS Grids!</h1>
<h2>Heading 2</h2>
<h3>Heading 3</h3>
<p>I'm vertically &amp; horizontally centered text over a full-sized page background-image.</p>
</div>
</body>
</html>

Hello,

please send us a link to your website in question, so we can better help.

Hans-Günter