In the Database Preferences you can specify the name of a custom CSS file to load. This would be the best place to place all of the CSS updates for that database. You can also point this to a single corporate CSS style for consistency.
For more details see: Database Preferences
In this CSS file you can add the following to change the button widths.
width: 400px; /* was 200px */
text-align: left; /* Add Left Alignment */
You can also use the following width if you want the buttons full width:
width: calc(100% - 10px);