レスポンシブでmargin-bottomが適用できるようにしたい。

前提・実現したいこと

発生している問題・エラーメッセージ

1200pxではmargin-bottomが効くが、750px以下だとmargin-bottomが効かない。

該当のソースコード

php
1<div class="main">
2    <!-- メインコンテンツ -->
3    <div class="main-contents">
4        <div class="main-contents__box">
5            <div class="main-contents__list" id="main" itemprop="mainContentOfPage" itemscope="itemscope" itemtype="http://schema.org/Blog">
6                <?php if (have_posts()) : while (have_posts()) : the_post(); ?>
7                        <article class="main-contents__block" itemscope="itemscope" itemtype="http://schema.org/BlogPosting" itemprop="blogPost">
8                            <figure class="main-contents__image">
9                                <span itemscope itemtype='http://schema.org/ImageObject' itemprop="image">
10                                    <a href="<?php the_permalink(); ?>" itemprop='contentUrl'>
11                                        <?php if (has_post_thumbnail()) : ?>
12                                            <?php the_post_thumbnail('full', array('itemprop' => 'image')); ?>
13                                        <?php else : ?>
14                                            <img src="https://placehold.jp/600x400.png" alt="">
15                                        <?php endif; ?>
16                                    </a>
17                                </span>
18                            </figure>
19                            <meta itemprop="about" content="<?php echo get_post_meta($post->ID, _aioseop_description, true); ?>">
20                            <section class="main-contents__texts">
21                                <p class="main-contents__time"><?php the_time('Y/m/d'); ?> (更新日: <?php the_modified_date('Y/m/d'); ?>)
22                                </p>
23                                <p class="category" itemprop="keywords"><a href="<?php the_permalink(); ?>">
24                                        <?php the_category(','); ?>
25                                    </a>
26                                </p>
27                                <h2 class="entry-title" itemprop="name headline">
28                                    <a href="<?php the_permalink(); ?>" title="<?php printf(the_title_attribute('echo=0')); ?>" itemprop="url">
29                                        <?php the_title(); ?>
30                                    </a>
31                                </h2>
32
33                                <p class="main-contents__description" itemprop="description"><?php the_excerpt(); ?></p>
34                            </section>
35                            <p class="btn"><a href="<?php the_permalink(); ?>">READ MORE</a></p>
36                        </article>
37                    <?php endwhile; ?>
38                <?php endif; ?>
39            </div>
40        </div>
41    </div>
42</div>

sass
1.main-contents__block {
2            list-style: none;
3            border: 1px solid $main;
4            border-radius: 5px;
5            overflow: hidden;
6            box-shadow: 0 0 8px gray;
7            @include btn();
8            text-align: center;
9            &:not(:last-child){
10                margin-bottom: 30px;
11            }
12            .main-contents__image {
13                overflow: hidden;
14
15                a {
16                    img {
17                        width: 100%;
18                        object-fit: cover;
19                        background-size: cover;
20                        display: block;
21                        transition-duration: 0.3s;
22                        height: auto;
23                        &:hover {
24                            transform: scale(1.1);
25                            transition-duration: 0.3s;
26                        }
27                    }
28                }
29            }
30
31            .main-contents__texts {
32                word-break: break-all;
33                padding: 60px;
34                text-align: center;
35
36                .main-contents__time {
37                    margin-bottom: 10px;
38                }
39                .category{
40                    margin-bottom: 10px;
41
42                }
43                h2,h1 {
44                    margin-bottom: 30px;
45                    a {
46                        color: $main-contents_a;
47                        font-size: 30px;
48                        line-height: 1.5;
49                    }
50                }
51                .main-contents__description ,p{
52                        line-height: 1.75;           
53                }
54            }
55        }     
56    }

sass
1//レスポンシブ
2
3                .main-list__block {
4                    width: 100%;
5
6                    margin-bottom: 60px;
7
8                    &:first-child {
9                        margin-top: 30px;
10                    }
11
12                    a {
13                        .main-block__image {
14                            width: 100%;
15                            img {
16                                background-size: cover;
17                                height: 100%;
18                            }
19                        }
20                    }
21
22                    h2 {
23                        
24
25                        a {
26                            display: block;
27                            padding: 30px;
28                            margin: 80px 0;
29                        }
30                    }
31                }
32