Quark modular: First module not overlaying hero image

Hello,
I'm using the quark theme and I've worked with the Quark One-Page site” skeleton to make my home page look good. here is the website i'm working on : https://walbike.omlet.ovh/

I'm trying to understand but can't figurate out how do you make the first modular content to stand out on the hero image ?
Just like on that screenshot :

Also, do you know why my hero image has so low quality? It's litterally a professional picture..

Thank you for your help,

@Delo,

Two remarks first:

• Please keep your title succinct. I've taken the liberty to alter it.
• Your second question is not related to the post's title and will be buried.

No overlap of hero and first module:
The problem can be found between your chair and keyboard. When using Quark out of the box, it is working just fine. But when you start removing required css classes from elements, things might brake. Start comparing the DOM of the original Quark skeleton and your site to find the differences.

It’s litterally a professional picture

The picture might be shot by a professional, but the size of the version used on your site is only 800x533 pixels. That is no "professional" grade in itself. Also, the device you are using might need way more pixels to fill the screen what degrades the quality even further.

@pamtbaau thank you for answering. Sorry for my english, it is not my main language.

1) The overlap disapear when I remove the features on the _highlight from one page quark skeleton. It doesn't happen when I remove some CSS. That's why i don't understand how removing them influences the overlap

2) The picture is 5472x3648 pixels and 14,9mb. When I upload it the quality automaticaly reduces. It looks like something is resizing it. Any idea where i could disable that?

Thank you for taking the time to understand me

@Delo:
The picture is 5472x3648 pixels and 14,9mb. When I upload it the quality automaticaly reduces. It looks like something is resizing it. Any idea where i could disable that?

Once again, please do not ask two unrelated questions in the same topic.