The non-flat toolbars had each button separate, with its own border. IE 3 did away with the borders. (Also seen in Office 97 vs 95, for example.) Compare the s

The non-flat toolbars had each button separate, with its own border. IE 3 did away with the borders. (Also seen in Office 97 vs 95, for example.) Compare the screenshots: https://upload.wikimedia.org/wikipedia/en/c/c5/Internet_Explorer_3_on_Windows_95.png https://upload.wikimedia.org/wikipedia/en/c/c5/Internet_Expl... https://upload.wikimedia.org/wikipedia/en/b/b3/Internet_Explorer_2.PNG https://upload.wikimedia.org/wikipedia/en/b/b3/Internet_Expl... or in Office: https://upload.wikimedia.org/wikipedia/en/4/4a/Office_97_on_Windows_NT_4.0.png https://upload.wikimedia.org/wikipedia/en/4/4a/Office_97_on_... https://upload.wikimedia.org/wikipedia/en/9/92/Office_95_on_Windows_NT_4.0.png https://upload.wikimedia.org/wikipedia/en/9/92/Office_95_on_...