Assistance in Theme Padding

Im building a site https://dartsforsale.com which is based on the Oswald Market Theme from Themeforest.

The specific page causing concern is https://dartsforsale.com/darts-info/mounting-a-dartboard/ where you can see the text goes right to the paaage edges. I have been told that i can use left and right padding to bring it in from the edge, making it more readable.

My skill levels are VERY basic, if someone can advise exactly what i have to do and where to do it, i would be extremely thankful. Hopefully i can just cut ^ paste ??

The second issue is that the site looks ok in firefox but in Chrome the header / Logo is much smaller and misplaced to the left. I dont even have a clue what to do do rectify this. Any advice on this would be awesome.

Thanks for your attention Guys ??