Diagonal Line Pattern made by only html/css. This is created using linear-gradient as the background of the body tag. It can also be implemented on a div if you want to use this pattern on a selected area only. The main key here is the background-size property which decides the thickness of the diagonal lines and this can be very helpful in creating different types of patterns.
Found this code at cssdeck by chocolatina, thought it might be useful.
Here you'll be able to place external scripts in the <head> section of the webpage.
Search for more libraries at https://cdnjs.com/
Link to Code