What wrong whith tumbs images in portfolio section when I look on it on tablet or when I reduce size of browser window?

Hi Siarhei,
The devices have resolution that is lower than 767px, we will use the style of the mobile, known as responsive style. Therefore, the thumbnail in the portfolio section is 100 % width. If you want to limit the width of the thumbnail in the section when the devices have resolution lower than 767 px, try adding the following code to Dashboard / Appearance / Customizer / Custom code / Header code

<style>
@media (max-width:767px) {
 body #main .portfolio .block {
 max-width: 240px;
 margin-left: auto !important;
 margin-right: auto !important;
 }
}
</style>

Hope this helps!