Here is a table of HTML codes and their CSS equivalent, for every day use.
These codes are good for both posts and widgets.

Text Formatting

Format HTML Code CSS Code
bold text <b> <b> OR <strong> </strong> font-weight: bold;
italic text <i> <i> OR <em>< /em> font-style: italic;
underlined text <u> </u> text-decoration: underline;
deleted text <del> </del> text-decoration: line-through;
linked text <a href=”#”> </a>
to open link in a new tab   <a href=”#” target=”_blank”> </a>
centered text
<center> </center> text-align: center;

Word spacing

Single   Space *nbsp;
Double   Space *emsp;

The * represents & for formatting reasons I cannot use the & or it will not show

Line Break

Next Line Break <br>
Double Line Break <br style=”clear:both;” />

Please Note: clear: both; denies the specific element to float right or left.

Images & Positioning

The generic code for images is the following:
<img src="#" alt="" />

This will link to your image as it is, static. However, you can also play with that generic HTML code to make images float left or right and adapt with the text wrapping around it.

Left position Right position
<img style=”float: left; margin-right: 5px;” src=”#” alt=”” /> <img style=”float: right; margin-left: 5px;” src=”#” alt=”” />