Which option uses a semantic keyword to create a CSS style instead of a specified class or id$?$

#footer $\{$

background$-$color: #bada$55$;

$\}$

bottom $\{$

background$-$color: #bada$55$;

$\}$

$.$footer $\{$

background$-$color: #bada$55$;

$\}$

footer $\{$

background$-$color: #bada$55$;

$\}$