Without further information I suspect you originally selected the standard text 'Text Appears' which has the grey background.
Ensure you are displaying the timeline, look at the text object on the timeline you will see it has two parts - the top part is the grey image the lower part the text.
Select the text object and Ungroup it using the broken kink icon above the timeline.
Select the upper part of the text object and delete it.
You should now be left with the text only.
To get text only select the General option, as shown in your image, and click in the preview monitor - this will insert the text object on the timeline at the point where the timeline marker is. You can then type in the text and add any effects you requre.
The example shown is made with one of the options under Title - Captions. The grey rectangle is a separate item on a track over the text. After Ungrouping them you can delete it.
Or you can make the text with Title - General or Standard