Bear BIKES | Landing page FCC responsive design

Hi guys!
I just finished my landing page after a long and (sometimes) painful time. I would appreciate if anyone could give some feedback on how the code is written and on the design of the website and, it may be a silly question, but how can I give my page a more professional look? I’ve re-done it twice, just because I thought it looked blanked, and in the future I would like to have some guidelines to avoid doing this again.
Also there is a weird bug when working with the Chrome device toolbar. For some reason when I check responsiveness for different resolutions, it displays the page incorrectly or different from what I see when I just manually resize the window for the same resolution. That said I don’t know how well the bikes will align for some of you, but let me know if the page displays wierdly and I will try to fix it.
For mozilla I’ve seen that my title underlines are very slim, and my images do not re-size the way I want. I have no idea how to fix these and if anyone knows, I will be very thankful to know.