Modifying Twenty Fifteen

author-removal.php

<?php
	// Author bio.
	if ( is_single() && get_the_author_meta( 'description' ) ) :
		get_template_part( 'author-bio' );
	endif;
?>

borderless.css

.borderless {
    padding:0px;
    box-shadow:none;
    background:transparent;
}

.borderless .entry-content {
    padding:0px; 
}

.borderless .entry-footer {
    display:none;
}

box-color.css

.hentry {
    background: #f4df30;
}

.entry-footer {
    background: #303030;
    color: #fff;
}

.entry-footer a {
    color: #fff;
}

image-credit.css

.after-post-section h3 {
    color: #333;
    font-size:1.3rem;
    display:inline-block;
    font-family: 'Noto Sans', sans-serif;
    font-weight:700;
    margin: 0 0 1em 0;
    line-height: 1.2;
    opacity:0.7;
    text-transform: uppercase;
    vertical-align: baseline;
}

.after-post-section h3::before {
    content: "";
    display: block;
    width: 100%;
    min-width: 30px;
    border-top: 1px solid #ddd;
    margin-bottom: 1em;
}

.after-post-section .section-content {
    font-size: 0.8em;
}

image-credit.html

<div class="after-post-section">
	<h3>Image Credit</h3>
	<div class="section-content">
		IMAGE CREDIT HERE
	</div>
</div>

image-credit.php

add_action( 'the_content', 'my_image_credit', 12 );
function my_image_credit( $content ) {
    if( is_singular() ) {
        $image_credit = get_field( 'image_credit' );
        if( !empty( $image_credit ) ) {
            $content .= '<div class="after-post-section"><h3>Image Credit</h3><div class="section-content">' . $image_credit . '</div></div>';
        }
    }

    return $content;
}

post-class-hook.php

add_filter( 'post_class', 'borderless_post_class' );
function borderless_post_class( $classes ) {
    global $post;
    if( get_field( 'borderless', $post->ID ) ) {
        $classes[] = 'borderless';
    }

    return $classes;
}

sidebar-location.css

@media screen and (min-width: 59.6875em) {
	.site-content {
		float: left;
		margin-left: 0px;
		width: 70.5882%;
	}
	
	.sidebar {
		float: right;
		right:0;
		margin-right: 0px;
		max-width: 413px;
		width: 29.4118%;
	}
	
	body:before {
		right: 0;
		left:auto;
	}
	
	.site-footer {
		margin: 0 0 0 6.1%;
	}

}