the problem here that background "#1B2827" in ".language-option" doesn't want to go full height after "#night-mode-toggle" switch: <style>
body,
html {
scrollbar-width: 2em;
scrollbar-color: #fada38 #000000;
overflow-x: hidden;
color:black;
margin: 0;
padding: 0;
position: absolute;
top: 0px;
left: 0px;
right: 0px;
bottom: 0px;
line-height: 1.6;
transition: background-color 2s, color 3s;
    --overflow:hidden;

}

header {
background-color: #4caf50;
color: #fff;
padding: 16px 0px 0px 0px;
text-align: center;
position: absolute;
transition: background-color 2s;
  width: 100%;
height: 18px;
right: 0px;
  z-index:999;
}

h1 {
margin: 0 auto;
display: flex;
justify-content: space-between;
align-items: center;
font-size: 18px;
width: 90%;
height: 1%;
}

  .background {
font-weight: bold;
padding: 0px;
text-align: center;
justify-content: center;
align-items: center;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
z-index: -1;
position: relative;
    display: flex;

}
  
.background:before {
content: '🇬🇧&nbsp;🇩🇪';
font-size: 10em;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
opacity: 0.15;
  display: flex;
 white-space: nowrap;
}
  .background-text {
display: flex;
flex-direction: column;
justify-content: center;
align-items: center;
position: relative;
    
z-index: -1;
}

.left::before,
.right::before {
content: "";
position: absolute;
top: 5px;
border-bottom: 1px dashed #fff;
width: 40%;
}

.left::before {
right: 100%;
margin-right: 20px;
}

.right::before {
left: 100%;
margin-left: 20px;
}

.flags-container {
  width: 100%;
position: relative;
top: 0;
right: 0px;
padding: 1px 0;
background-color: darkgreen;
display: flex;
justify-content: center;
align-items: center;
--box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
z-index: 1;
}

.flag-radio {
display: none;
}

.flag-label {
cursor: pointer;
margin: 0 5px;
transition: 0.3s;
opacity: 0.6;
font-size: 24px;
}

.flag-label:hover {
opacity: 1;
}

.language-option {
position: absolute;
top: 0px;
left: 0px;
right: 0px;
bottom: 0px;
display: none;
justify-content: center;
align-items: center;
padding-top: 64px;
  width: 100%;
height: 100%;
  background-color: white;
}

#english-flag:checked ~ #english,
#hindi-flag:checked ~ #hindi,
#hebrew-flag:checked ~ #hebrew,
#chinese-flag:checked ~ #chinese,
#french-flag:checked ~ #french,
#spanish-flag:checked ~ #spanish {
display: block;
}

#night-mode-toggle:checked ~ body,
#night-mode-toggle:checked ~ header,
#night-mode-toggle:checked ~ .language-option,
#night-mode-toggle:checked  {
background-color: #1B2827;
color: #F3EFEF;text-shadow: 1px 1px 2px rgba(42, 81, 21, 0.5);
}


.switch-container {
position: absolute;
top: 5px;
right: 16px;
display: flex;
align-items: center;
  justify-content: center;
z-index: 2;
}

.switch-container label {
    content: "&#x1F319;";
position: relative;
margin-left: 0px;
cursor: pointer;
user-select: none;
  align-items: center;
  justify-content: center;
}

.switch {
  content: "&#x1F319;";
position: relative;
cursor: pointer;
width: 64px;
height: 32px;
margin-right: 5px;
background-color: darkgreen;
border-radius: 15px;
transition: background-color 3s;
}

.switch:before {
  content: "🌿";
display: block;
position: absolute;
top: 2px;
left: 2px;
height: 0px;
width: 0px;
background-color: #121;
border-radius: 50%;
transition: left 1s;
}

#night-mode-toggle:checked ~ .switch-container .switch {
background-color: #121;
}

#night-mode-toggle:checked ~ .switch-container .switch:before {
left: calc(100% - 28px);content: "🌙";
}

p {
margin: 15px 5px;
--x-blend-mode: Overlay;
color: rgba(243, 239, 239, 0.5);
  background-color: #182C2B;
  padding:5px 15px;
  border-radius:10px 10px;
text-shadow: 0px 0px 6px 6px rgba(27,40,39,1);
box-shadow: 0px 0px 10px 20px rgba(0, 0, 0, 0.2);
  z-index:1;
}

h2 {
width: 100%;
display: flex;
flex-direction: column;
justify-content: center;
align-items: center;
font-size: 1.5rem;
font-weight: bold;
--margin: 1em 0;
color: #721336;
text-shadow: 0px 0px 8px rgba(0, 0, 0, 0.5);
background-color: #182C2B;
--padding: 0.5em 1em;
--border-radius: 0 10px 10px 0;
--box-shadow: 0px 0px 5px 10px rgba(10, 100, 10, 0.1);
--opacity: 0.8;
  z-index:2;
}

@media only screen and (max-width: 600px) {
h2 {
font-size: 1.5rem;
padding: 0.5em 0.75em;
}
}
</style>
</head>
<body>

<input id="english-flag" type="radio" name="flags" class="flag-radio">
<input id="hindi-flag" type="radio" name="flags" class="flag-radio">
<input id="hebrew-flag" type="radio" name="flags" class="flag-radio">
<input id="chinese-flag" type="radio" name="flags" class="flag-radio">
<input id="french-flag" type="radio" name="flags" class="flag-radio">
<input id="spanish-flag" type="radio" name="flags" class="flag-radio">

  <div class="flags-container"><logo id="supercrazylogotype"></logo>
<label for="english-flag" class="flag-label">🇬🇧</label>
<label for="hindi-flag" class="flag-label">🇮🇳</label>
<label for="hebrew-flag" class="flag-label">🇮🇱</label>
<label for="chinese-flag" class="flag-label">🇨🇳</label>
<label for="french-flag" class="flag-label">🇫🇷</label>
<label for="spanish-flag" class="flag-label">🇪🇸</label>
</div>

<header>
<h1>
<span class="left">EcoWare</span>
<span class="right">Earthwise</span>
</h1>
</header>

<!-- Night Mode Switch -->
<input type="checkbox" id="night-mode-toggle" />
<div class="switch-container">
  <label for="night-mode-toggle">
    <div class="switch"></div>
  </label>
</div>

<div id="english" class="language-option">
<p>Our mission</p>
</div>

<div id="hindi" class="language-option">
<p>hindi details going here</p>
</div>

<div id="hebrew" class="language-option">
<p>hebrew details going here</p>
</div>

<div id="chinese" class="language-option">
<p>chinese details going here</p>
</div>

<div id="french" class="language-option">
<p>french details going here</p>
</div>

<div id="spanish" class="language-option">
<p>spanish details going here</p>
</div>
<span class="background">
<span class="background-text">
</span>
</span>
</body>
</html>