HTML: Change the font size of the Blogger Post Title

 tried a new theme for my blogger (http://btecho.blogspot.com/). Everything was fine, except for the post title. When I’m in the home page of my blog I got this large text post title, but when I click on one of my post, the post title font changes and the size of it becomes small. . 

I played around the css code, and tried to edit the following. I tried changing the .post h3 a,.post h3 a:visited,.post h3 strong to .post h2 a,.post h2 a:visited,.post h2 strong, and this .post h3 a,.post h3 a:visited,.post h3 strong. Nothing happened, And the other lines of codes I also tried to modify it to see if there is changes. The part of the codes for post section of the HTML file were I played around is shown below. I really appreciate if anyone of you can help me on this. BTW, I’m beginner on HTML. Thanks!

.post {
margin:0 0 25px;
}

.post h3 a,.post h3 a:visited,.post h3 strong {
display:block;
color:#333333;
font-family:Cuprum, arial, serif;
font-size:30px;
line-height:1.3;
text-decoration:none;
}

.post h3 strong,.post h3 a:hover {
color:#333333;
}