WordPressサイトのedgeでのバグ解消

前提・実現したいこと

edgeでのHTML/CSSの挙動をchremeやsafariと同じにしたい。

発生している問題・エラーメッセージ

WordPressでWebサイトを制作しています。
url:brace-gym.com
概ね出来上がっているのですが、edgeでの挙動が思った通り行きません。
該当箇所はトップページになるのですが、下記コードの箇所箇所の<div>内の<a>がhover時にz-indexにマイナス補正が掛かったような挙動をします。

該当のソースコード

HTML
1<div class="largemenu section">
2 <div class="largemenu-item">
3  <div class="largemenu-item-inner mask">
4   <a href="https://brace-gym.com/?page_id=160">料金表</a>
5  </div>
6 </div>
7 <div class="largemenu-item">
8  <div class="largemenu-item-inner mask">
9   <a href="https://brace-gym.com/?page_id=404">店舗イメージ</a>
10  </div>
11 </div>
12 <div class="largemenu-item">
13  <div class="largemenu-item-inner mask">
14   <a href="https://brace-gym.com/?page_id=304">スタッフ紹介</a>
15  </div>
16 </div>
17 <div class="largemenu-item">
18  <div class="largemenu-item-inner mask">
19   <a href="https://brace-gym.com/?page_id=418">見学・入会案内</a>
20  </div>
21 </div>
22 <div class="largemenu-item">
23  <div class="largemenu-item-inner mask">
24   <a href="https://brace-gym.com/?page_id=162">ご利用について</a>
25  </div>
26 </div>
27 <div class="largemenu-item">
28  <div class="largemenu-item-inner mask">
29   <a href="https://brace-gym.com/?page_id=164">会社概要</a>
30  </div>
31 </div>
32</div>

css
1.mask {
2	color: #fff;
3}
4.mask p,
5.mask a,
6.mask ul,
7.mask h2,
8.mask h3,
9.mask h4 {
10	position: relative;
11	z-index: 3;
12}
13.mask:after {
14	content: '';
15	display: block;
16	position: absolute;
17	height: 100%;
18	width: 100%;
19	top: 0;
20	left: 0;
21	background-color: rgba(0, 0, 0, .5);
22	color: #fff;
23	z-index: 1;
24}
25
26.largemenu .largemenu-item:nth-of-type(1) .largemenu-item-inner {
27	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/calculator-1156121_1920.jpg');
28}
29.largemenu .largemenu-item:nth-of-type(2) .largemenu-item-inner  {
30	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/couple-1298432_1280.jpg');
31}
32.largemenu .largemenu-item:nth-of-type(3) .largemenu-item-inner  {
33	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/adult-2449725_1920.jpg');
34}
35.largemenu .largemenu-item:nth-of-type(4) .largemenu-item-inner  {
36	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/woman-1730325_1920.jpg');
37}
38.largemenu .largemenu-item:nth-of-type(5) .largemenu-item-inner {
39	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/questions-2212771_1280.jpg');
40}
41.largemenu .largemenu-item:nth-of-type(6) .largemenu-item-inner {
42	background-image: url('https://brace-gym.com/wp-content/uploads/2018/12/office-3295556_1280.jpg');
43}
44.largemenu {
45	margin-top: -10px;
46	margin-bottom: 5px;
47	display: flex;
48	justify-content: space-between;
49	flex-wrap: wrap;
50}
51.largemenu .largemenu-item {
52	flex-basis: calc(50% - 5px);
53	margin-top: 10px;
54	position: relative;
55}
56.largemenu .largemenu-item .largemenu-item-inner {
57	height: 100%;
58	width: 100%;
59	transition-duration: .3s;
60}
61.largemenu .largemenu-item .largemenu-item-inner:hover {
62	opacity: .5;
63	transition-duration: .3s;
64	z-index: 2;
65}
66.largemenu .largemenu-item .largemenu-item-inner:before {
67	content: '';
68	position: absolute;
69	top: 5px;
70	left: 5px;
71	height: calc(100% - 12px);
72	width: calc(100% - 12px);
73	border: 1.25px solid #fff;
74	z-index: 2;
75}
76.largemenu .largemenu-item a {
77	display: block;
78	height: 100%;
79	width: 100%;
80	text-align: center;
81	color: #fff;
82	line-height: 80px;
83	font-weight: bold;
84	letter-spacing: 1px;
85}
86.largemenu .largemenu-item .largemenu-item-inner {
87	height: 100%;
88	width: 100;
89	background-size: cover;
90	background-position: center;
91}
92@media screen and (min-width:600px) {
93	.largemenu .largemenu-item {
94		flex-basis: calc(33.3% - 5px);
95	}
96	.largemenu .largemenu-item a {
97		line-height: 100px;
98	}
99	.largemenu .largemenu-item .largemenu-item-inner:before {
100		height: calc(100% - 17px);
101		width: calc(100% - 17px);
102		top: 7.5px;
103		left: 7.5px;
104	}
105}
106@media screen and (min-width:960px) {
107	.largemenu .largemenu-item a {
108		line-height: 130px;
109	}
110	.largemenu .largemenu-item .largemenu-item-inner:before {
111		height: calc(100% - 22px);
112		width: calc(100% - 22px);
113		top: 10px;
114		left: 10px;
115	}
116}