I was looking for a way to edit my Email Font Size and Style in Gmail, unluckily there is none. Luckily there are now Canned Responses. This makes it easy to save a a template and then use it for your Emails.
1. Start by setting up the Canned Responses extension: Click Settings in the right top corner of your Gmail page -> Ctrl + F to open the search ob the browser and type: "Canned Responses", this will take you down the page to the extension -> Enable it -> Scroll to the Bottom and "Save" the settings!
2. In your Compose Mail Mask you now have next to "Attach a File" and "Add event invitation" the Canned Responses extension (with a small drop down arrow)
3. Create Your Text you can use the Rich formatting which is useful, but very limited. If you want to get fancy my suggestion is create something nice in Word or any other Text Formater and then copy it into this Email.
4. Click on the small Canned Responses arrow and save your Email Template.
5. Whenever you open the Compose Mail Page "Open" your Canned Response and your settings will appear. Unfortunately you can't set it to load automatically, but this gives you the option to choose your Template according to who you are sending your Email to!
My suggestion is not to bother with a Signature because it's not possible to format your Text there. Instead set up your Signature in your Canned Response just like in the image below. Another tip is: If you get an email and like the style that is used by the respective person simply copy that email into a fresh Composed Email, delete the text and adjust the Signature, and then save it as one of your Email Templates (aka Canned Responses). This saves you the hassle of going through the editing yourself and chances are the style used is more advanced than what the Rich Formatting in Gmail offers.
This Email Style was copied from Guy Kawasaki, thank you so very much for that Guy, it feels very comfortable and warm.