Side Bar ad

CSS is usually a separate file, but it can be in the HTML tag. So you'll be looking at something like this.

<img src="advert.jpg" alt="Sidebar Advert" class="advert">

IMG tag displays the image. SRC is the source, so point that to where your image is located. Alt is the name of the image. Class is the CSS to apply to the image.

Any CSS you have goes in the CSS file, something like

.advert {
width: 300px;
height: 600px;
border: 2px solid black;
}

If you don't have access to the CSS file then you can adjust your HTML img tag to include the style, however, this isn't recommended.

<img src="advert.jpg" alt="Sidebar Advert" style="width: 300px; height: 600px; border: 2px solid black;">

Does that help? Without more information, it's hard to help more.

I suspect you won't need the CSS if you have the jpg/png of the ad you want. So you might just need:

<img src="advert.jpg" alt="Sidebar Advert">