Website Lost, Please Help :'(

Hi

I am very new to building my own website. Everything was going great until I tried changing the font size of my title banner.

I went through the dashboard, Appearances, Editor, then the Customisation tab.

I pasted what I thought was the right code right at the bottom, updated and lost my site,
so i went back in and deleted what i had pasted but may have deleted an extra line by mistake, not knowing updated again, now I have totally lost my site.

Can any one help me?
https://www.liampickup.com was my sight