How to get rid of boxing in css of ASP.NET web application?

.Iam new to making a ASP.NET Core web application and i have most of it finished however I've come across a styling issue,where I cannot fit the size of some of the elements to the fill width of the screen.Ive tried the css + html code separately to the ASP.NET and it works fine. Thanks.  Link to ASP.NET version  Picture of the Html/CSS of the ASP.NET  Working one with elements taking full screen size