Tumblr posters cannot adjust the font size for the text in a Tumblr text post as of January 2014. Though you can edit a text post in HTML mode, most code is stripped from the form when the post is published. However, you can adjust the size of the font on your Tumblr blog theme. Use the Tumblr HTML editor to modify the “font-size" property in your blog theme CSS code for the element you want to change.

Step 1

Log in to Tumblr and select the blog that hosts your audio player widget to open the blog in the dashboard.

Step 2

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

Step 3

Press “Ctrl-F” to open the Find tool, then type “font-size” in the Find box. The first instance of “font-size” is highlighted in the code. Click the down arrow to find each instance of the “font-size” property until you locate the element to modify. For example, if you want to change the size of the title, change the value of the font-size attribute in the #wrapper #title section.

Step 4

Type the new font size over the existing entry. For example, if the existing entry is “font-size: 15px,” change the ”15px“ entry to a smaller number to decrease the font size. Change the value to a larger number to increase the size of the font.

Step 5

Click the “Update Preview” button to view your changes in the Preview window.

Step 6

Click “Save” to save the edits, then click “Exit” to close the Customize tool.