Font size troubles

Hi I’m a novice at this sort of stuff and I was hoping someone could help me out

I cant seem to change any of the font sizes in my appearance editor ccs page.

I try to change the title of my page by changing it with this bit of code.

.page-title,
.comments-title,
.comment-reply-title,
.post-navigation .post-title {
font-size: 18px;
font-size: 1.8rem;
line-height: 1.3333;

But nothing happens

and i try to change the widget text size with

.widget {
font-size: 14px;
font-size: 1.4rem;

this bit of code and nothing happens

Do i need to change the sidebar border or something?

any help would be greatly appreciated, apologies for my ignorance of coding

[ Moderator note: Code block deleted, please do not post hundreds of lines of code in these forums. ]