Minor fixes!

Hi all! I received a few questions regarding the mobile menu, so I went ahead and (tried) to make it generally more responsive and easier to play around with as well as added a few quality of life improvements :)

• Made a few tweaks to the function menu and mobile menus to make them more responsive
• Added a label to the CSS mobile menu section
• Added styling for the HR (Horizontal Ruler/Line) element
• Separated the light and dark mode colors in the root menu