How do I change the like and reblog button colors with this code?

Trying to change tumblr like and reblog button colors, the only code I found related to them is this. Adding in "color: #;" didn't change anything. What would I need to write for the colors to change?

<pre>
.reblog_button,
.like_button iframe {
    width: {text:Font Size} !important; /* calc fallback */
    height: {text:Font Size} !important; /* calc fallback */
    width: calc({text:Font Size} + 2px) !important;
    height: calc({text:Font Size} + 2px) !important;
</pre>

Apologies if this is a stupid question, started learning HTML very recently, still a beginner.