How to make an image full width in container block

I have set up container blocks so I can show different blocks depending on devices. I want a full width image on mobile for one block. I have made the padding 0 on the container block, and put an image block inside. The image does not reach the edges. There is still a remaining 15px padding.

I have tried adding a custom CSS class, but it does not apply. If I add:

.athemes-blocks-block-container-wrapper-content {
padding-right: 0px !important;
padding-left: 0px !important;
}

to the Custom CSS, it works, but then affects all blocks. If I give the same CSS a custom class name, it does not apply, not in the customizer or on the front end.

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