corrected custom.css file by adding dot notation-symbolizes class

[harshithaMMPS333]

The CSS class selector in custom.css was missing the dot (.) notation.
Because of this, the styles were not applied correctly in the browser.

added the proper dot prefix so the class is recognized as a valid CSS class selector.
This ensures the styling behaves as intended.

Before:
article p img, FeatureCallout
article iframe {
display: block;
margin-left: auto;
margin-right: auto;
max-width: 50%;
}

After:
article p img,
.FeatureCallout
article iframe {
display: block;
margin-left: auto;
margin-right: auto;
max-width: 50%;
}