understrap/inc/extras.php

<?php
/**
 * Custom functions that act independently of the theme templates.
 *
 * Eventually, some of the functionality here could be replaced by core features.
 *
 * @package understrap
 */

if ( ! function_exists( 'understrap_body_classes' ) ) {
	/**
	 * Adds custom classes to the array of body classes.
	 *
	 * @param array $classes Classes for the body element.
	 *
	 * @return array
	 */
	function understrap_body_classes( $classes ) {
		// Adds a class of group-blog to blogs with more than 1 published author.
		if ( is_multi_author() ) {
			$classes[] = 'group-blog';
		}
		// Adds a class of hfeed to non-singular pages.
		if ( ! is_singular() ) {
			$classes[] = 'hfeed';
		}

		return $classes;
	}
}
add_filter( 'body_class', 'understrap_body_classes' );

// Removes tag class from the body_class array to avoid Bootstrap markup styling issues.
add_filter( 'body_class', 'adjust_body_class' );

if ( ! function_exists( 'adjust_body_class' ) ) {
	/**
	 * Setup body classes.
	 *
	 * @param string $classes CSS classes.
	 *
	 * @return mixed
	 */
	function adjust_body_class( $classes ) {

		foreach ( $classes as $key => $value ) {
			if ( $value == 'tag' ) {
				unset( $classes[ $key ] );
			}
		}

		return $classes;

	}
}

// Filter custom logo with correct classes.
add_filter( 'get_custom_logo', 'change_logo_class' );

if ( ! function_exists( 'change_logo_class' ) ) {
	/**
	 * Replaces logo CSS class.
	 *
	 * @param string $html Markup.
	 *
	 * @return mixed
	 */
	function change_logo_class( $html ) {
		$html = str_replace( 'class="custom-logo"', 'class="img-responsive"', $html );
		$html = str_replace( 'class="custom-logo-link"', 'class="navbar-brand custom-logo-link"', $html );

		return $html;
	}
}