@samednakhla You can definitely put styles in the page header.
If you are looking to add styles just for a particular page, this is where to do that:
If you want to add styles which you would be able to access from any page, go to Settings > SEO / metatags > Advanced settings > Script/meta tags in the header.
Whichever you end up using, make sure you include the HTML
<style> tag like this:
/* Your CSS goes here */
Now that you know how, here’s also a word of warning based on my experience. I use this approach quite a lot, but it’s not a panacea. Bubble’s antiquated approach of absolute positioning of elements on the page will quickly make you go crazy once you start applying your custom CSS. A good rule of thumb is that tweaking positioning and responsiveness usually breaks things, whereas changing what the element looks like doesn’t. Fingers crossed their upcoming switch to Flexbox fixes the former for good, but until then, it is what it is.