Using this post , you can add welcome message to
your blog.



Log in to your blogger account and Go to Design >> Edit HTML
Put checked marked in Expand Widget Templates
Find this tag by using Ctrl+F    ]]></b:skin>
 Paste below code after ]]></b:skin> tag

.element { position:fixed; bottom:1%; right:1%; padding:10px; font-family:Arial;
 background:#98DBF7; border:1px solid #2FBAF6; }

 Now Go to Design >>page Element

Click Add gadget  and Select HTML/JavaScript 

Now paste paste below code

<div class="element">... Message Here ...</div>

Replace Blue color sentence with your own message
Now save  HTML/JavaScript.  you are done.