Usei o flexbox

Some feedback:

• you should better organise your projects by grouping your stylesheets into a folder, the images used into another one;
• when using several images as background images, think of grouping them into a single one, in other words think of image sprites (check this page on MDN);
• in your HTML, you defined the language used with lang="pt-br" in the html root element, but since the page is in English, and not in Brazilian Portuguese, you should write lang="en";
• you should enhance the semantics of the HTML, by using the header element to wrap the page header;
• you should group the two sibling h1s on the header into one;
• for each section in the main part of the page, you should use h2 instead of h1: it is generally not recommended to have multiple h1s in a single page;
• when defining font sizes, avoid using pixels and use relative units instead such as rem (here is a video explaining why);
• since you used Sass, you could have refactored the CSS rules to declare the top borders of each box (in Sass, you can do it using the @each rule).

I hope this feedback helps you.