Use font-weight: bold or font-weight: 700 to request bold text. normal corresponds to 400. Other numeric weights let you request intermediate or heavier faces, but the visible result depends on the font.

Working example

Compare normal and bold weightsLink

HTML and CSS

HTML

<p class="normal">Bring your project notes.</p>
<p class="bold">Bring your project notes.</p>

CSS

.normal {
  font-weight: 400;
}
.bold {
  font-weight: 700;
}

Edit HTML or CSS to update the preview as you type. Copy code snippet copies the selected tab. Preview spacing and font defaults are not included.

Both paragraphs have the same semantics. CSS changes their appearance. Use strong when the words express importance, and b when drawing attention without adding that importance.

The requested weight may not exist

Modern syntax permits numeric values from 1 through 1000. Variable fonts can supply ranges; static font families often have only a few faces. The browser matches an available face or may synthesize weight. A request for 500 is not a guarantee of a distinct medium face, and not every value above 400 is synonymous with bold.

Inspect the loaded font files and computed font-weight if weights look identical. Use valid CSS comments such as /* bold */; // is not a browser CSS comment.

Sources

Reference 1 Reference 2 provide the technical details and current compatibility information.