You can edit your Tumblr theme in any way you would like using the Tumblr HTML editor. Tumblr themes use the “<div>” tag to specify sections in the theme. You can add an extra column, such as a sidebar, to your theme using a combination of Cascading Style Sheets -- or CSS code -- and HTML code. Define a table in one of your <div> sections, then add rows using the <tr> tags. Add cells to the rows with <td> tags.

Define a Sidebar Column

Step 1

Open your Tumblr dashboard, then select the blog to modify in your dashboard.

Step 2

Click “Customize,” then click “Edit HTML” to open the HTML editor.

Step 3

Define the column by inserting the following code between the "<style type="text/css">" and “</style>” tags in the CSS section of the theme code. You can style the sidebar, as desired, but the code below provides the base construct for the column:

.sidebar { position: relative; left: 0px; top: 0px; }

Step 4

Insert the following code between the “<div id="wrapper">” and corresponding “</div>” tags in the body section of the HTML code where you want the column to appear. Replace the text “(Insert Your Sidebar Content Here)” with your own content.

<div class="sidebar"> ...(Insert Your Sidebar Content Here)... </div>

Step 5

Click “Update Preview,” then click “Save” to save your changes. Click “Exit” to close the Customize menu.

Define a Table with Rows

Step 1

Open the theme code in the Tumblr HTML editor, then locate the <div> tag that you will use for your table. Create a new “<div>” section, if desired.

Step 2

Insert the following code to define the new table. Replace “Cell 1,” “Cell 2,” etc. with your content. Use CSS styles to format the table, as desired.

   &lt;table&gt;
        &lt;tr&gt;&lt;td&gt;Row 1, Cell 1&lt;/td&gt;&lt;td&gt;Row 1, Cell 2&lt;/td&gt;&lt;/tr&gt;
        &lt;tr&gt;&lt;td&gt;Row 2, Cell 3&lt;/td&gt;&lt;td&gt;Row 2, Cell 4&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;

Step 3

Click “Update Preview,” then click “Save” to save your changes. Click “Exit” to close the Customize menu.