Using linked CSS is easier to change colors and background if you keep the same extrusion.
Linked CSS is the recommended model, because in this template all the code
CSS is in a separate file and can be linked to several pages
website. This is the best model to promote the reuse of
code.
However in the case of email avoid using external CSS.
- Some email clients do not accept. Both in HEAD, and in
BODY.** Use CSS inline (right in the element), but do not abuse
Properties like position, float and etc...
- All images should have display:block, so it prevents Gmail and Hotmail from adding a spacing between them.
- Do not use style="color: #fff"; Use style="color: #ffffff";
- CSS3 / HTML5: Feature a very low compatibility rate, so they are not recommended.
- Finally remember to avoid using Divs if your template has multiple columns, in this case tables are the most reliable tool.
- You should not build your entire template on images because some email programs block the viewing of these images.
Source
Note the following table that shows what is most advised to use in the various email clients
See also this website will show the tags you should or should not use on the various email clients
On the google page you can also find this useful information about the operation of gmail
There are tools that convert the linked CSS code into inline CSS giving the following example
@Renan Yes, but kind as that CSS is used, inline, embedded or external?
– Leonardo Bonetti
I would like to know what the best practice is, but I do not know why you have already denied the question...
– Leonardo Bonetti
Many email services do not carry external and embedded sheets. You may use them, but it is at your own risk.
– Renan Gomes
@So I will stylize inline even, thank you.
– Leonardo Bonetti