Header and footer font style latex

The fancyhdr documentation just puts font specifications inside the argument of fancyhead/fancyfoot. The following does that, but stores your font declarations inside a user defined macro, so that you only have to change it in one place.

documentclass[a4paper,12pt,twoside]{book}
usepackage[utf8]{inputenc}
usepackage[english]{babel}
usepackage{fancyhdr}

newcommand*myheaderfooterfont{normalfontbfseriessffamily}

pagestyle{fancy}
fancyhf{}
fancyhead[LE,RO]{myheaderfooterfont Overleaf}
fancyhead[RE,LO]{myheaderfooterfont Guides and tutorials}
fancyfoot[CE,CO]{myheaderfooterfont leftmark}
fancyfoot[LE,RO]{myheaderfooterfont thepage}

renewcommand{headrulewidth}{2pt}
renewcommand{footrulewidth}{1pt}

begin{document}

chapter{Using different page styles}

Lorem ipsum dolor sit amet, consectetur adipiscing ...

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do 
eiusmod tempor incididunt ut labore
pagebreak
 This details the set of real numbers and its subsets such as natural numbers, integers, rational numbers, constructible numbers, algebraic numbers and irrational numbers. Students or learners should be in a position to define all proper subsets of real numbers and should be in a position to tell the proper inclusion. Further, students should master the axioms obeyed by natural numbers, integers, rational numbers and real numbers. Such axioms or laws form a constitution which learners will then apply to justify results just like in court of laws. Using the axioms or the given constitution of real numbers or its subsets, learners should follow logic and use them to establish propositions, lemmas and theorems. Thus rigorous proofs of results emanates from such axiom. Understand the concept of real numbers as a complete ordered field. Define such terms as a lower bound, an upper bound, minimum value, maximum value, infimum and supremum of a given set of real numbers. These are the key in the establishment of results in all the remaining chapters for this course. From the aforementioned definitions be in a position to state and prove the characterization of infimum and supremum. Extend real numbers to the concept of countability of sets. Here you should be in a position to apply Cantor's diagonal method for the case of rational numbers.
 et dolore magna aliqua. Ut enim 
ad minim veniam, quis nostrud exercitation ullamco laboris nisi 
ut aliquip ex ea commodo consequat. Duis aute irure dolor in 
reprehenderit in voluptate velit es...

end{document}