Change sidebar date and title

Sign into Blogger (Dashboard), click LAYOUT > EDIT HTML to open the template editor and search for this:

.sidebar h2 {
etc. etc.
}

etc. etc. means whatever may be in between { and } but which is not relevant to this post

Edit it (add a line) to read

.sidebar h2 {
background-color:blue;
etc. etc.
}

If you cannot find

.sidebar h2 {
etc. etc.
}

Then just add this:

.sidebar h2 {
background-color:red;
}

(or any color rather than red or any other HTML color code

to anywhere before

]]<>/b:skin<

but preferably just after:

/* Sidebar Content
----------------------------------------------- */

so that it is together with others in the template which is related to the sidebar. That section of the template will then look like this:

/* Sidebar Content
----------------------------------------------- */
.sidebar h2 {
background-color:red;
}