As you are new, it's best not to pick up bad habits which, unfortunately is easy to do because so much of the code out there is just copied and pasted by folks who don't know any better, so:
Try not to write inline styles or inline event handlers like this:
<button style="background-color:lightgreen;width:230;height:70;border: none; font: bold 25px GreatVibes;" onclick="history.go(0)">Inspire Me More!</button>
As you can see, it makes the code difficult to read as there are 3 languages in that one element!
Instead, separate your languages into their own sections, or even files.
With regard to CSS styles, it would be better to define CSS classes ahead of time and then just switch to the class you need, rather than write all that inline CSS.
You also have some errors in your code.
So, here's an updated version of your code that also changes the font. Make sure to review the comments for details.
<html>
<head>
<title>Daily Quotes</title>
<style>
/* We'll separate the CSS into this section and prepare pre-made classes for styles.
See how much cleaner this is, not only here but in the HTML as well? */
button {
background-color:lightgreen;
width:230;height:70;
border: none;
font: bold 25px GreatVibes;
}
.share {
background-color:blue;
width:200px; /* Don't forget to add the unit */
height:70px; /* Don't forget to add the unit */
}
#output {
/* Now, just the output area has its own style! */
font-family: fantasy;
}
</style>
</head>
<body>
<!-- All your content must be between the opening and closing body tags. -->
<h1>Inspirational Quotes</h1>
<div>
<button>Inspire Me More!</button>
</div>
<div>
<button class="share">Share</button>
<img src="images/bg.jpg" id="bg" alt="">
</div>
<!-- Don't use document.write() to inject content into a page. Instead, prepare an
element ahead of time that you will update later. -->
<div id="output"></div>
<!-- Place your script tags just before the closing of the body tag. That way, you can be
sure that any HTML element you reference in the script has already been read into memory. -->
<script>
// First, get references to the HTML elements you'll want to work with:
var btn = document.querySelector("button");
var out = document.getElementById("output");
// Then, set up your event handlers in JavaScript, not in HTML
btn.addEventListener("click", getQuote);
function getQuote(){
// Here's a simpler way to set up an array:
var theQuotes= [
'Whenever you see a successful business, someone once made a courageous decision. - Peter Drucker',
'If you\'re not part of the solution, you\'re part of the problem. - African Proverb',
'When you confront a problem you begin to solve it. - Rudy Giuliani',
'Dream of painting and then I paint my dream. - Vincent Van Gogh',
'Be silent or let thy words be worth more than silence. - Pythagoras',
'The past cannot be changed. The future is yet in your power. - Mary Pickford',
'Anything\'s possible if you\'ve got enough nerve. - J.K. Rowling'
];
// You only want your radom number to be from 0 to the amount of the quotes array -1
var quoteNum = Math.floor(Math.random() * theQuotes.length);
// Now, just update the prexisting element:
output.textContent = theQuotes[quoteNum];
}
</script>
</body>
</html>
element.style.font = "bold 25px GreatVibes"