Well for a start You need to visualize the layout the way you want it.
what I mean by that think of "DIV's" as "main" they help to layout your websites the way you want to see your page, they are like containers or "divides" if you want to call it,
judging by the image I'd say at least +- 5 DIV's to begin with obviously it depends on peoples style that changes the number of DIV's but if it was me i'd use at least 4 to 5 DIV's for this.
Now to answer your questions.
border-radius:; to apply the rounded borders be wary they don't work on most older browsers so if you are not concerned for that than border Radius is your friend :).
In my mind that can be best achieved using
<ul></ul> tags simply styling them to either
display:inline-block; for newer browsers or
float:left but please be wary there are rules applied to float elements as they are a little bit problematic for people who is learning css or re-learning css. Otherwise make use of a div layout like so DIV | DIV bellow the heading and to avoid them from warping you can use % along with
box-sizing:border-box that piece of code is used to tell the browser to calculate the width to make sure padding's are used within the equation so that width doesn't change when adding padding .
Doing that would just mean adding another DIV with
text-align:center and obviously your text required.
If you are concerned for the color being too boring maybe consider using texture If you are the designer of the game than you could always create your own texture to give it a bit of style. But if you must use images simply don't go overboard doing this requires the
Background-image:URL(); code while in brackets place the file location of the image.
This is my favourite website to learn coding https://www.w3schools.com/css/ obviously some people would disagree with me perhaps there are some tutorials on this site where you can learn css I am not even 100% familiar with this site yet either
I gave these pointers since you said you are willing to learn again this site can very well help you if you run into some coding issues.