In case you haven't found it yet and it might help someone else, you need to read
https://developers.google.com/chart/interactive/docs/gallery/table?hl=en#configuration-options
There are three parts to getting CSS styles to work in tables.
1) Set the HTML and CSS in options
2) Define the class names
3) Write the styles
The options should contain at a minimum
var options = {
allowHtml: true,
cssClassNames: cssNames
};
Then using whatever you called the cssClassNames (I used cssNames, but it can be whatever you want)
var cssNames = {
'headerRow': 'headercss',
'tableCell': 'cellcss'
};
Then write the styling for whatever you called the CSS classes
<style>
.cellcss {
text-align: left;
padding: 10px;
}
.headercss {
background-color: blue;
text-transform: uppercase;
color: white;
}
</style>