EDITING THE DESIGN OF YOUR BLOG USING CSS ON BLOGGER

WAY 1:

The CSS section of a Blogger template is typically between <b:skin> and </b:skin>. The opening <b:skin> should have an arrow on the side means that it is “folded”. If you click the arrow, it will expand and show you the CSS. The end of this is </b:skin> which is usually after the styling code for mobile. In between these <b:skin> & </b:skin> is where you will find all of the styling for your blog.

WAY 2:

You can add CSS anywhere between <b:skin> & </b:skin> but typically it is better to add it at the end, above </b:skin>. 
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You can easily add CSS to the Blogger Template Designer (Template > Advanced > Add CSS), once you add the code hit enter and save. This will get added to the bottom of the CSS, just before </b:skin>.
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If you want to edit existing CSS, it is better to edit the original code rather than adding more. It just makes it neater and easier for browsers to read.

There are other easy ways of adding CSS styling to blogger while dealing with HTML5.

WAY 3:

Inline - by using the style attribute in HTML element

An inline CSS is used to apply a unique style to a single HTML element. It uses the style attribute of an HTML element. This example sets the text color of the <h1> element to blue:

<h1 style="color:blue;">This is a Blue Heading</h1>