Rework the overall design to follow Angular.dev look & feel

[pBouillon]

Angular went through major changes in its branding and overall look, mainly on the new docs but also by reworking its logo

It might be great for the update guide to follow the trends and use the newest colors (the gradient thing) as well as the new logo

This might not be mission critical but it's always nice to work with pretty tools, even if that's mostly subjective!