Hello,
Try to add this code in Global Custom CSS section:
.header-wrapper .menu > li > a {
padding-top: 10px;
padding-bottom: 5px;
}
For mobile version, you can write some code in Theme Options > Custom CSS > Custom CSS for mobile.
As for product page, try to disable all 3-rd party plugins, clear browser cache, and check the issue.
In your case you need to use css code. For example, to change styling for all links use the following code in Theme Options > Custom CSS > Global Custom CSS section:
a:hover {
text-decoration: underline;
color: red;
}
Regards,
Rose Tyler.